U.S. patent number 8,388,546 [Application Number 12/427,244] was granted by the patent office on 2013-03-05 for method of locating the tip of a central venous catheter.
This patent grant is currently assigned to Bard Access Systems, Inc.. The grantee listed for this patent is Peter M. Rothenberg. Invention is credited to Peter M. Rothenberg.
United States Patent |
8,388,546 |
Rothenberg |
March 5, 2013 |
Method of locating the tip of a central venous catheter
Abstract
Methods of locating a tip of a central venous catheter ("CVC")
relative to the superior vena cava, sino-atrial node, right atrium,
and/or right ventricle using electrocardiogram data. The CVC
includes at least one electrode. In particular embodiments, the CVC
includes two or three pairs of electrodes. Further, depending upon
the embodiment implemented, one or more electrodes may be attached
to the patient's skin. The voltage across the electrodes is used to
generate a P wave. A reference deflection value is determined for
the P wave detected when the tip is within the proximal superior
vena cava. Then, the tip is advanced and a new deflection value
determined. A ratio of the new and reference deflection values is
used to determine a tip location. The ratio may be used to instruct
a user to advance or withdraw the tip.
Inventors: |
Rothenberg; Peter M. (San
Clemente, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Rothenberg; Peter M. |
San Clemente |
CA |
US |
|
|
Assignee: |
Bard Access Systems, Inc. (Salt
Lake City, UT)
|
Family
ID: |
41164558 |
Appl.
No.: |
12/427,244 |
Filed: |
April 21, 2009 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20090259124 A1 |
Oct 15, 2009 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
PCT/US2009/033116 |
Feb 4, 2009 |
|
|
|
|
11552094 |
Oct 23, 2006 |
7794407 |
|
|
|
61026372 |
Feb 5, 2008 |
|
|
|
|
Current U.S.
Class: |
600/508; 600/510;
607/28; 600/509 |
Current CPC
Class: |
A61B
5/063 (20130101); A61B 5/061 (20130101); A61B
5/065 (20130101); A61B 5/25 (20210101); A61B
5/287 (20210101); A61B 5/349 (20210101); A61B
5/06 (20130101) |
Current International
Class: |
A61B
5/02 (20060101) |
Field of
Search: |
;600/508,509,510
;607/28,122 |
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|
Primary Examiner: Patel; Niketa
Assistant Examiner: El-Kaissi; Hiba
Attorney, Agent or Firm: Rutan & Tucker, LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION(S)
This application is a continuation of International Application
PCT/US09/033116, filed Feb. 4, 2009, which designated the U.S. and
that International Application was published under PCT Article
21(2) in English. This application also includes a claim of
priority under 35 U.S.C. .sctn.119(e) to U.S. provisional patent
application No. 61/026,372, filed Feb. 5, 2008, now expired, and a
claim of priority under 35 U.S.C. .sctn.120 to U.S. patent
application Ser. No. 11/552,094, filed Oct. 23, 2006, now U.S. Pat.
No. 7,794,407.
Claims
The invention claimed is:
1. A method of determining a location of a tip of a central venous
catheter having a lumen filled with an electrolytic material, a
portion disposed inside the superior vena cava, and a first
electrode in communication with the electrolytic material, the tip
having an opening in communication with the lumen that exposes the
electrolytic material inside the lumen to the electrical
environment outside the tip, the method comprising: attaching a
second electrode to the skin of a subject, positioning the tip of
the central venous catheter within the superior vena cava; while
the tip is positioned within the superior vena cava, obtaining a
reference electrical signal comprising the voltage difference
between the first electrode and the second electrode; generating a
reference P wave from the reference electrical signal; determining
a reference deflection value of the reference P wave; one of
advancing and withdrawing the tip of the central venous catheter to
a new position; while the tip is in the new position, obtaining a
new electrical signal comprising the voltage difference between the
first electrode and the second electrode; generating a new P wave
from the new electrical signal; determining a new deflection value
of the new P wave; calculating a ratio of the new deflection value
to the reference deflection value; comparing the ratio to a
threshold value; and one of advancing or withdrawing the tip based
on the comparison of the ratio to the threshold value.
2. The method of claim 1, wherein the one of advancing or
withdrawing the tip based on the comparison of the ratio to the
threshold value comprises: advancing the tip if the ratio is less
than the threshold value; and withdrawing the tip if the ratio is
greater than the threshold value.
3. The method of claim 1, wherein the threshold value is less than
a ratio of a deflection value of a P wave detectable near the
sino-atrial node to the reference deflection value.
4. The method of claim 1, further comprising: if the ratio is equal
to the threshold value, maintaining the tip of the central venous
catheter in its current position.
5. The method of claim 1, further comprising: if the ratio is
greater than the threshold value, comparing the ratio to a second
threshold value, and if the ratio is greater than the second
threshold value, determining the tip of the central venous catheter
is in the right atrium and withdrawing the tip.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed generally to devices for and
methods of locating a catheter inside a body and more particularly
to devices for and methods of locating the tip of a central venous
catheter inside the superior vena cava, right atrium, and/or right
ventricle using information obtained from an electrocardiogram.
2. Description of the Related Art
Central venous catheters ("CVC") include any catheter designed to
utilize the central veins (e.g., subclavian and superior vena cava)
or right sided cardiac chambers for the delivery and/or withdrawal
of blood, blood products, therapeutic agents, and/or diagnostic
agents, CVCs also include catheters inserted into the central veins
or right sided cardiac chambers for the acquisition of hemodynamic
data. Standard central venous catheters for intravenous access,
dialysis catheters, percutaneously introduced central catheters
("PICC" lines), and right heart ("Swan-Ganz.TM.") catheters are
examples of CVCs.
The standard of care for placing a CVC (other than right heart
catheters which generally terminate in the pulmonary artery)
dictates that the tip of the CVC lie just above and not inside the
right atrium. In fact, in 1989, the Food and Drug Administration
issued a warning citing an increased risk of perforation of the
right atrium, clot formation, and arrhythmias among other potential
complications resulting from the tip of the CVC being placed inside
the right atrium.
While CVCs have been used for many years, determining the position
of the tip of the CVC has always been problematic. Currently, a
chest x-ray is used to determine the position of the tip of the
CVC. Because CVC may be a radiopaque and/or include radiopaque
materials, the CVC is visible on an x-ray. However, this method has
several drawbacks. For example, obtaining a chest x-ray is labor
intensive and expensive. In recent years, CVCs, which were
traditionally placed in a hospital in-patient setting, are being
placed in an outpatient setting more frequently. In an outpatient
setting, obtaining a chest x-ray to determine the position of the
tip of the CVC can be very cumbersome and may not be obtained in a
timely manner. Therefore, using a chest x-ray to determine the
position of the tip of the CVC may introduce a considerable delay,
prolonging the procedure. Generally, the operator will leave the
patient to perform other duties while the x-ray is processed. If
the tip is improperly placed, the operator must return to the
patient's bedside to reposition the CVC. To reposition the CVC, the
operator must open the sterile dressing, cut the sutures,
re-suture, and redress the wound, all of which potentially expose
the patient to discomfort and infection.
Recently, navigational systems principally used to guide
peripherally placed lines have become available. Based upon the
detection of magnetic fields between a stylet tip and a detector,
these systems assume (and depend upon) a relationship between
surface landmarks and anatomic locations. Unfortunately, these
systems cannot be used to determine the location of the tip of a
CVC with sufficient accuracy because the relationship between
surface landmarks and anatomic locations is highly variable from
one patient to another.
In addition to the need to know where the tip is during initial
placement, the CVC may migrate or otherwise move after the initial
placement and require re-positioning. Therefore, the operator must
monitor or periodically reevaluate the location of the tip.
An electrocardiogram ("ECG") measures electrical potential changes
occurring in the heart. Referring to FIGS. 1A-1C, the ECG
measurements may be visualized or displayed as an ECG trace, which
includes ECG waveforms. As is appreciated by those of ordinary
skill in the art, ECG waveforms are divided into portions that
include a QRS complex portion and a P wave portion in addition to
other wave portions. The QRS complex corresponds to the
depolarization of the ventricular muscle. The P wave portion of the
ECG waveforms represents atrial muscle depolarization; the first
half is attributable to the right atrium and the second half to the
left atrium. Under normal circumstances, atrial muscle
depolarization is initiated by a release of an excitatory signal
from the sino-atrial ("SA") node, a specialized strip of tissue
located at the juncture of the superior vena cava ("SVC") and right
atrium.
As is appreciated by those of ordinary skill in the art, an ECG may
be obtained using different electrode configurations. For example,
a standard configuration referred to as "Lead II" may used. In a
bipolar Lead II configuration, one of the electrodes (the cathode)
is attached to the left leg and the other electrode (the anode) is
attached to the right shoulder. As is appreciated by those of
ordinary skill in the art, using a different configuration could
change the polarity and/or the shape of the P wave. Other standard
bipolar configurations include a bipolar Lead I configuration where
the cathode is attached to the left shoulder and the anode is
attached to the right shoulder and a bipolar Lead III configuration
where the cathode is attached to the left leg and the anode is
attached to the right shoulder.
The waveforms depicted in FIGS. 1A-1C and 2B were obtained using
the anode of a standardized bipolar ECG Lead II configuration
attached to the right shoulder and the tip of the CVC as the
cathode. While technically this configuration is not a standard
Lead II configuration, the trace produced by the electrodes 114A
and 114B may be displayed on a standard ECG monitor using the
monitor's circuitry to display the trace as a bipolar Lead II
trace.
Techniques of using ECG waveforms to locate the tip of a CVC have
been available since the 1940s. Some of these prior art devices
construct an intravascular ECG trace by placing an electrode near
the tip of the CVC and using that electrode to measure the voltage
near the tip of the CVC relative to a surface electrode(s) and/or a
second electrode spaced from the first.
These techniques have shown that both the magnitude and shape of
the P wave change depending upon the positioning or location of the
electrode attached to the tip of the CVC. Referring to FIGS. 1A and
1B, two exemplary ECG traces are provided for illustrative
purposes.
FIG. 1A is an ECG trace made when the electrode attached to the tip
of the CVC is in the proximal SVC. This tip location corresponds to
position "1" depicted in FIG. 2A. The portion of the ECG trace
corresponding to an exemplary P wave produced when the electrode
attached to the tip is located in position "1" is labeled "P1."
FIG. 1B is an ECG trace made when the electrode attached to the tip
of the CVC is approaching the SA node and stops at a location
adjacent to the SA node. These tip locations correspond to moving
the tip from a position "2" to position "3" depicted in FIG. 2A.
The portion of the ECG trace corresponding to an exemplary P wave
produced when the electrode attached to the tip is approaching the
SA node is labeled "P2" and the portion of the ECG trace
corresponding to an exemplary P wave produced when the electrode
attached to the tip is located adjacent to the SA node is labeled
"P3."
Normally as the electrode attached to the tip of the CVC moves from
the proximal SVC (position "1") toward the SA node (position "3"),
the maximum value of the absolute value of the voltage of the P
wave increases dramatically. When the electrode attached to the tip
of the CVC is adjacent to the SA node (position "3"), the voltage
of the P wave (please see "P3" of FIG. 1B) reaches a maximum value
that is more than twice the value experienced in the proximal SVC
and may be as large as eight times the voltage in the proximal SVC.
When this occurs, the tip of the CVC is considered to have entered
into the right atrium. Because the magnitude of the P wave more
than doubles when the electrode attached to the tip of the CVC is
adjacent to the SA node, this information may be used to place the
tip of the CVC within a few centimeters (e.g., about 1 cm to about
2 cm) proximal to the SA node. Additionally, as the electrode
attached to the tip of the CVC moves from the proximal SVC toward
the right atrium, the shape of the P wave changes from a "u" shape
(FIG. 1A) to a spike-like shape (FIG. 1B).
Referring to FIG. 2B, another exemplary illustration of the P wave
portion of the ECG trace produced when the electrode attached to
the tip of the CVC is located at positions 1-5 depicted in FIG. 2A
is provided. The P wave portions of the ECG traces of FIG. 2B are
labeled with the letter "P" and occur between the vertical dashed
lines. Each of the exemplary traces is numbered to correspond to
positions "1" through "5." Therefore, the ECG trace "1" was
produced when the electrode attached to the tip was located in the
proximal SVC. The trace "2" was produced when the electrode
attached to the tip was in position "2" (distal SVC). The trace "3"
was produced when the electrode attached to the tip was adjacent to
the SA node.
As the electrode attached to the tip of the CVC is advanced further
into the right atrium, the polarity of the P wave "P" changes from
predominantly negative near the top of the right atrium (position
"3") to isoelectric (i.e., half has a positive polarity and half
has a negative polarity) near the middle of the right atrium
(position "4") to almost entirely positive at the bottom of the
right atrium (position "5"). These changes in the P wave "P" are
illustrated in traces "3" through "5."
FIG. 1C is an ECG trace made when the electrode attached to the tip
of the CVC is in the right ventricle. The portion of the ECG trace
corresponding to an exemplary P wave produced when the electrode
attached to the tip is labeled "P6." When the electrode attached to
the tip of the CVC is advanced into the right ventricle, the
maximum magnitude of the absolute value of the P wave "P6"
approximates the maximum magnitude of the absolute value of the P
wave "P1" when the electrode attached to the tip of the CVC was
inside the proximal SVC above the SA node (i.e., located at
position "1"). However, the polarity of the first half of P wave
"P6," which corresponds to the right atrium, is opposite.
The first technique developed for viewing the ECG waveform during
the insertion of a CVC used a column of saline disposed within a
hollow tube or lumen longitudinally traversing the CVC. The column
of saline provides a conductive medium. Saline was inserted into
the lumen by a saline filled syringe with a metal needle. The
needle of the syringe remained within the entrance to the lumen or
port in contact with the column of saline after the lumen was
filled. One end of a double-sided alligator clip was attached to
the needle and the other end was attached to an ECG lead, which in
turn was attached to an ECG monitor. By using the saline solution
filled CVC as a unipolar electrode and a second virtual electrode
generated by ECG software from three surface electrodes, an
intravascular ECG was obtained. The operator would adjust the
position of the tip of the CVC based on the magnitude and shape of
the P wave displayed by the ECG monitor.
Subsequently, this technique was modified by substituting an
Arrow-Johans adapter for the metal needle. The Arrow-Johans adapter
is a standard tubing connector with an embedded conductive ECG
eyelet. The Arrow-Johans adapter may be placed in line with any
conventional CVC. In a closed system, the tubing and CVC may be
filled with saline, i.e., a conductive medium, and the CVC used as
a unipolar electrode in conjunction with surface electrodes and a
standard ECG monitor. The ECG eyelet is placed in contact with the
saline in the lumen of the CVC. One end of the ECG lead is attached
to the ECG eyelet and the other end to the ECG monitor for
displaying the intravascular ECG waveforms. Because the system must
be closed to prevent the saline from leaking out, this system works
best after the guide wire used to thread the CVC forward has been
withdrawn, i.e., after placement has been completed. Therefore,
although the catheter may be withdrawn after initial placement, it
may not be advanced into proper position.
BBraun introduced its Certofix catheter to be used in conjunction
with its Certodyne adapter. In this system, a patch lead with two
ends has an alligator clip connected to one end. The alligator clip
is clipped to the CVC guide wire. The other end of the patch lead
includes a connector that is plugged into the Certodyne adapter.
The ECG may be obtained during placement and the catheter may be
advanced or withdrawn as desired. However, the Certodyne adapter
has many moving parts and is not sterile, making the procedure
cumbersome to perform and the operative field more congested.
Additionally, the sterile field may become contaminated by the
non-sterile equipment.
The Alphacard, manufactured by BBraun, merges the Arrow-Johans
adapter and the Certodyne adapter. The Alphacard consists of a
saline filled syringe (used to flush the CVC with saline) and a
connector to the Certodyne. The Alphacard is used to obtain a
`snapshot` of the ECG trace from the saline column. If an atrial
spike is seen in the ECG trace, the CVC is withdrawn.
With respect to all of these prior art methods of using an ECG
trace to place the tip of the CVC, some degree of expertise is
required to interpret the P waves measured because the user must
advance the guide wire slowly and watch for changes in the P wave.
If the catheter is inserted too far too quickly and the changes to
the P wave go unnoticed (i.e., the operator fails to notice the
increase or spike in the voltage experienced when the electrode
attached to the tip is in the right atrium), the operator may
mistakenly believe the tip is in the SVC when, in fact, the tip is
in the right ventricle. If this occurs, advancing the tip may
injure the patient.
U.S. Pat. Nos. 5,078,678 and 5,121,750 both issued to Katims teach
a method of using the P wave portion of an ECG trace to guide
placement of the tip of the CVC. The CVC includes two empty lumens
into which a transmission line is fed or an electrolyte is added.
Each of the lumens has a distal exit aperture located near the tip
of the CVC. The two exit apertures are spaced from one another. In
this manner, two spaced apart electrodes or a single anode/cathode
pair are constructed near the tip of the CVC. The voltage or
potential of one of the electrodes relative to the other varies
depending upon the placement of the electrodes. The voltage of the
electrodes is conducted to a catheter monitoring system. The
catheter monitoring system detects increases and decreases in the
voltage of the P wave. The voltage increases as the electrodes
approach the SA node and decrease as the electrodes move away from
the SA node. Based on whether the voltage is increasing or
decreasing, the operator is instructed by messages on a screen to
advance or withdraw the CVC.
While Katims teaches a method of locating the tip of a CVC relative
to the SA node, Katims relies on advancing or withdrawing the CVC
and observing the changes of the P wave. Katims does not disclose a
method of determining the location of the tip of the CVC based on a
single stationary position. Unless the entire insertion procedure
is monitored carefully, the method cannot determine the position of
the tip of the CVC. Further, the Katims method may be unsuitable
for determining the location of a previously positioned stationary
tip.
Other devices such as Bard's Zucker, Myler, Gorlin, and CVP/Pacing
Lumen Electrode Catheters are designed primarily to pace. These
devices include a pair of electrodes at their tip that are
permanently installed and designed to contact the endocardial
lining. These devices include a lumen, which may be used to deliver
and/or withdraw medications or fluids as well as for pressure
monitoring. These leads are not designed for tip location and do
not include multi-lumen capability.
A method of obtaining an intravascular ECG for the purposes of
placing a temporary pacing wire was described in U.S. Pat. No.
5,666,958 issued to Rothenberg et al. Rothenberg et al. discloses a
bipolar pacing wire having a distal electrode. The distal electrode
serves as a unipolar electrode when the pacing wire is inserted
into the chambers of the heart. The pacing wire is connected to a
bedside monitor through a specialized connector for the purposes of
displaying the ECG waveforms detected by the distal electrode.
Given the volume of CVCs placed yearly and the increasing demand
particularly for PICC lines (devices that permit the delivery of
intravenous therapeutic agents in the outpatient setting, avoiding
the need for hospitalization) a great need exists for methods and
devices related to locating the tip of a CVC. Particularly, devices
and methods are needed that are capable of determining the location
of the tip before the operator leaves the bedside of the patient.
Further, a method of determining the location (SVC, right atrium,
or right ventricle) of the tip from a single data point rather than
from a series of data points collected as the catheter is moved may
be advantageous. Such a system may be helpful during initial
placement and/or repositioning. A need also exists for a device for
or a method of interpreting the ECG waveforms that does not require
specialized expertise. Methods and devices that avoid the need for
hospital and x-ray facilities are also desirable A need also exists
for devices and methods related to determining the position of the
tip of the CVC that are less expensive, expose patients to fewer
risks, and/or are less cumbersome than the x-ray method currently
in use.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
FIG. 1A is an exemplary ECG trace obtained from an electrode placed
inside the proximal SVC.
FIG. 1B is an exemplary ECG trace obtained from an electrode
approaching the sino-atrial node and stopping adjacent thereto.
FIG. 1C is an exemplary ECG trace obtained from an electrode placed
inside the right ventricle.
FIG. 2A is an illustration of a partial cross-section of the heart
providing five exemplary tip locations 1, 2, 3, 4, and 5.
FIG. 2B is a series of exemplary P wave traces 1, 2, 3, 4, and 5
obtained from an electrode placed in each of the exemplary tip
locations 1, 2, 3, 4, and 5 depicted in FIG. 2A, respectively.
FIG. 3A is a signal analysis system configured to determine the
position of the tip of a CVC using a single pair of electrodes.
FIG. 3B is an embodiment of a CVC including three pairs of
electrodes.
FIG. 4 is a block diagram illustrating a method of using a single
pair of electrodes to locate the tip of the CVC within the SVC.
FIG. 5 is a block diagram illustrating a method of using a single
pair of electrodes to determine the tip of the CVC is located
within the right ventricle.
FIG. 6 is a block diagram illustrating a method of using a single
pair of electrodes to determine the location of the tip of the CVC
within the right atrium.
FIG. 7 is an embodiment of a signal analysis system for use with
the CVC of FIG. 3B.
FIG. 8 is a block diagram illustrating the components of the signal
analysis system of FIG. 7.
FIG. 9 is block diagram illustrating the components of a monitor of
the signal analysis system of FIG. 3A.
FIG. 10 is a block diagram illustrating a method of using at least
two pairs of electrodes to locate the tip of the CVC relative to
the SVC, right atrium, and right ventricle.
FIGS. 11A-11B are a block diagram illustrating an alternate method
of using a single pair of electrodes to locate the tip of the CVC
relative to the SA node.
DETAILED DESCRIPTION OF THE INVENTION
Central Venous Catheter 100
Aspects of the present invention are directed toward a device for
locating the tip of a central venous catheter ("CVC") and a method
of determining the location of the tip of a CVC. The embodiments
depicted in FIGS. 3A and 3B, include a CVC 100 constructed using
any manner known in the art from a flexible nonconductive material,
such as polyurethane or other suitable polymer material. It may
also be desirable to use a radiopaque material to construct the CVC
100. As is appreciated by those of ordinary skill in the art, the
material used to construct the CVC 100 may include materials and/or
coatings that provide improved anti-thrombotic or anti-bacterial
properties. The CVC 100 has a body 130 configured to be received
within a central vein. The body 130 may include a distal end 110
having a tapered tip 112 and a proximal end 120 spaced
longitudinally along the body 130 from the distal end 110.
Referring to FIG. 3A, the body 130 may include one or more lumens
132 that traverse the length of the body and may have one or more
openings 134 at or spaced from the tip 112 and an open end portion
122 configured to permit access into the lumen 132. When the tip
112 of the CVC 100 is received within a central vein, the open end
portion 122 may remain outside the central vein allowing materials
(e.g., saline, mediations, etc.) to be inserted into the lumen 132
while the tip 112 is inside the central vein or another anatomical
structure. The opening 134 permits the passage of materials between
the lumen 132 and the environment outside the CVC 100. If one or
more materials are inserted into the lumen 132 via the open end
portion 122, those materials may exit the lumen 132 via the opening
134. If materials enter the lumen 132 via the opening 134, those
materials may exit the lumen 132 via the open end portion 122.
The open end portion 122 is configured be coupled to a connector
124 through which materials may be introduced into or exit from the
open end portion 122 of the lumen 132. The connector 124 may
include any suitable connector known in the art including a
Tuohy-Borst adapter, stop cock, and the like. In the embodiment
depicted in FIG. 3A, the connector 124 is a Tuohy-Borst adapter,
which includes a side port 125 through which materials (e.g.,
saline) may be introduced into the open end portion 122 of the
lumen 132. The side port 125 may be used to flush the lumen 132
with normal saline or another material. The connector 124 is
configured to maintain materials within the lumen 132 and to
prevent those materials from leaking out of the CVC 100 through the
open end portion 122.
The lumens 132 may be used as conduits for the passage of materials
such as medications and/or other fluids to and from the environment
outside the CVC 100. For example, the lumen 132 may be used to
aspirate blood into the CVC 100 and/or provide a conduit through
which pressure data may be collected and used to construct pressure
waveforms. The environment outside the CVC 100 may include the
inside of the SVC, right atrium, and/or right ventricle. The CVC
100 is provided for illustrative purposes and those of ordinary
skill in the art appreciate that alternate embodiments of CVC 100
including embodiments with additional lumens, a flow directed
balloon tip, thermistors, thermodilution ports, pacing wire ports,
embedded pacing electrodes, and the like are within the scope of
the present invention.
Deflection Value
The deflection of an ECG trace, (i.e., its vertical height relative
to the baseline) may be used to compare two or more P waves.
Because a P wave constitutes a voltage change over time, the
deflection of the P wave is not constant. In particular
embodiments, the P wave is represented by an array or series of
discrete numerical values.
The deflection value may be calculated in several ways. For
example, the maximum or peak deflection may be used. Alternatively,
the deflection value may be calculated as the difference between
the maximum deflection and the minimum deflection. The deflection
value may also be calculated as the sum of the absolute value of
the maximum and minimum deflections. If the P wave has two peaks,
which may occur when the tip 112 is located within the right atrium
and the P wave is biphasic (see position 4 of FIGS. 2A and 2B), the
deflection value may be calculated by totaling the absolute value
of the two peaks. When this method is used, the deflection value of
the P wave measured at positions 3-5 may all be approximately
equal. Further, if discrete data is being used, the deflection
value may also be calculated as a total of the discrete deflection
quantities. If continuous data is being used, the deflection value
may also be calculated as the integral under the P wave. Further,
the deflection value may also be calculated as the average P wave
deflection. Because the polarity of portions of the P wave change
depending upon the location of the tip 112, it may be beneficial to
use the absolute value of the deflection of the P wave to calculate
the deflection value.
For the purposes of this application, the term "deflection value"
will be used hereafter to describe the metric used to compare two
or more P waves, which depending upon the implementation details
may be detected by one or more pairs of electrodes. It is
appreciated by those of ordinary skill in the art that the
deflection value may be determined in numerous ways including those
listed above and others not listed and the invention is not limited
by the method and manner of determining the deflection value of the
P wave.
In the embodiments discussed below, unless otherwise indicated, the
deflection value is calculated as the sum of the absolute value of
the maximum and minimum deflections when the maximum and minimum
deflections have opposite polarities. The deflection value is
calculated as the larger of the absolute value of the maximum and
minimum deflections when the maximum and minimum deflections have
the same polarity. In other words, the vertical height of the P
wave is used.
Embodiments Using a Single Pair of Electrodes
Referring to FIG. 3A, an embodiment of a system 121 using a single
pair of electrodes 114 to determine the position of the tip 112 of
the CVC 100 will be described. An electrolytic material or
solution, such as saline, may be disposed inside the lumen 132. The
electrolytic material inside the lumen 132 forms a continuous
conductor or column of electrolytic material that may be used to
conduct an electrical signal from the opening 134 in the tip 112,
and up the continuous column. In other words, the opening 134
exposes the electrolytic material inside the lumen 132 to
electrical activity occurring in the environment outside the tip
112. A first electrode 114A of the pair of electrodes 114 is placed
in electrical communication with the continuous column inside the
lumen 132. The first electrode 114A may be coupled by a wire 123 to
a monitor 127.
A second or surface electrode 114B is placed in contact with the
skin of a patient. By way of a non-limiting example, the surface
electrode 114B may be affixed to the skin of the patient's chest
using any method known in the art. The surface electrode 114B is
coupled to the monitor 127 by a wire 129. The voltage at or near
the opening 134 in the tip 112 may be measured using the pair of
electrodes 114.
The voltages detected by the pair of electrodes 114 may be used to
create an ECG trace of the electrical activity observed at or near
the tip 112 of the CVC 100. Because the voltage across each of the
pair of electrodes 114 may vary with time, the voltage across wires
123 and 129 may constitute a time-varying signal that can be
analyzed using standard signal processing methods well known in the
art. In a typical patient, the maximum voltage across the pair of
electrodes 114 may range from about 0.2 mV to about 3 mV. The
signal detected by the pair of electrodes 114 may be amplified
and/or filtered to improve the signal quality.
In the embodiment depicted in FIG. 3A, the first electrode 114A is
coupled to the connector 124. Alternatively, the first electrode
114A may be located inside at least a portion of the lumen 132. By
way of another example, the first electrode 114A is coupled to the
side port 125 through which the electrolytic material (e.g.,
saline) may be introduced into the open end portion 122 of the
lumen 132. As is apparent to those of ordinary skill in the art,
the first electrode 114A may be located anywhere that would place
it in electrical continuity or communication with the electrolytic
material (e.g., saline) exiting the tip 112 via the opening 134 or
otherwise communicating electrically with the environment outside
the opening 134 of the tip 112. By way of another example, the
first electrode 114A may be incorporated into a guide wire (not
shown), stylet, and the like that extends from, or near the tip 112
up the body 130 of the CVC 100 and is electrically coupled by the
wire 123 to the monitor 127. The monitor 127 is described in detail
below.
Method of Using a Single Electrode Pair to Determine the Position
of the Tip of the CVC
Referring to FIG. 4, a method 140 of determining the location of
the tip 112 using the pair of electrodes 114 will now be described.
In block 141, the CVC 100 is inserted into the SVC. The CVC 100 may
gain venous access to the SVC by any method known in the ad
including inserting the CVC 100 in a standard sterile fashion
through the subclavian, one of the jugular veins, or a peripheral
vein and directing the tip 112 of the CVC 100 through that vein
toward the proximal SVC.
Next, in block 142, a reference deflection value is recorded in a
storage location. The reference deflection value is the deflection
value obtained from the pair of electrodes 114 when the tip 112 is
located in the venous system proximal to or in the proximal
SVC.
Then, in block 143, the tip 112 is advanced. As the tip 112 is
advanced, a ratio of the deflection value of the currently observed
P wave to the reference deflection value is calculated. Inside the
SVC, as the tip 112 approaches the mid SVC, the deflection value of
the P wave may increase by two to four times the reference
deflection value. Further, as the tip 112 approaches the distal
SVC, the deflection value of the P wave may increase by four to six
times the reference deflection value. In the distal SVC near the SA
node, the deflection value of the P wave may increase by six to
eight times the reference deflection value.
In decision block 144, whether the ratio is less than or equal to a
first predefined threshold value is determined. The first
predefined threshold value should be large enough to ensure the tip
112 has left the proximal SVC and entered the mid SVC. Further, the
first predefined threshold value should be small enough to prevent
placement of the tip 112 in the distal SVC. Thus, the first
predefined threshold value may be within a range of about 1.6 to
about 3.9. By way of a non-limiting example, the first predefined
threshold value may be about 2.0. If the ratio is less than or
equal to the first predefined threshold value, in block 143, the
tip 112 may be advanced and the ratio recalculated. Ratio values
less than or equal to the first predefined threshold value indicate
the tip 112 is in the proximal or mid SVC and has not yet reached
either the distal SVC, caval-atrial junction adjacent to the SA
node or the upper right atrium.
If decision block 144 determines the ratio is not less than or
equal to the first predefined threshold value, the method 140
advances to decision block 145. In decision block 145, whether the
ratio is less than or equal to a second predefined threshold value
is determined. The second predefined threshold value should be
large enough to ensure the tip 112 is in the distal SVC and small
enough to avoid entry of the tip 112 into the right atrium. By way
of a non-limiting example, the second predefined threshold value
may within a range of about 4.0 to about 8.0. By way of a
non-limiting example, the second predefined threshold value may be
about 8.0. In other words, the block 144 determines whether the
ratio is between the first and second threshold values or within a
range defined between the first and second threshold values (e.g.,
about 2.0 to about 8.0). Nevertheless, ratio values within the
range defined between the first and second threshold values may
indicate the tip 112 is approaching or has reached the SA node, or
the tip is located within the right atrium. In other words, any
ratio value above the second predefined threshold value may
indicate the tip 112 is located in the distal SVC or the upper
atrium. If the ratio is within the range defined between the first
and second threshold values, the decision in decision block 145 is
"YES" and the method 140 ends.
If the ratio is greater than the second threshold value, the
decision in decision block 145 is "NO," and the method 140 advances
to block 147. When the ratio is greater than the second threshold
value, the tip 112 is in or near the right atrium and in block 147,
the user or operator is advised to withdraw the tip 112. By way of
a non-limiting example, the user or operator may be advised to
withdraw the tip 112 about 0.5 cm to about 1 cm. Then, in block
147, advancement of the tip 112 is terminated and the tip 112
withdrawn. By way of a non-limiting example, the user or operator
may withdraw the tip 112 about 0.5 cm to about 1 cm. In block 147,
as the tip 112 is withdrawn, the ratio of the deflection value of
the currently observed P wave to the reference deflection value is
recalculated.
Then, the method 140 returns to decision block 144.
In particular embodiments, if at any time during the performance of
method 140, the ratio is equal to the second predefined threshold
value, the tip 112 is maintained in its current position without
additional advancement or withdrawal and the method 140 ends. When
the method 140 ends, the ratio is between the first and second
threshold values and the tip 112 is located in the mid SVC or
distal SVC.
The following table, Table 1, summarizes the relationship between
the location of the tip 112 of the CVC 100 and the ratio of the
deflection value of the currently observed P wave to the reference
deflection value:
TABLE-US-00001 TABLE 1 Location of the tip 112 Very Distal Proximal
Mid Distal SVC or SVC SVC SVC Right Atrium Ratio: ratio of the
deflec- .ltoreq.1.5 1.6-4.0 4.1-5.5 >5.5-8.0 tion value of the
currently observed P wave to the reference deflection value
While Table 1 provides exemplary ranges and/or threshold values for
use as a general guideline, those of ordinary skill in the art
appreciate that these values may benefit from adjustment as
additional anatomic or electrophysiologic data is acquired and such
modified values are within the scope of the present invention.
As is apparent to those of ordinary skill, the pair of electrodes
114 may be used to detect the instantaneous location of the tip
112. Therefore, if the tip 112 migrates into the atrium, this
movement may be detected immediately by calculating a ratio of the
deflection value of the currently observed P wave to the recorded
reference deflection value and comparing the ratio to the first and
second threshold values. This calculation may be performed
periodically or at random intervals. If the tip 112 migrates into
the atrium, a medical professional may be alerted via a signal,
such as an alarm, and the like, to reposition the tip 112.
Referring to FIG. 5, a method 450 may be used to determine the tip
112 is located within the ventricle. In first block 452, the tip
112 is located in the atrium. Then, in block 454, a reference
atrium deflection value is recorded. The reference atrium
deflection value is the deflection value obtained from the pair of
electrodes 114 when the tip 112 is located in the atrium. Then, in
block 456, a ratio of the deflection value of the current P wave
detected by the pair of electrodes 114 to the reference atrium
deflection value is determined. In decision block 457, whether the
ratio is greater than a third predefined threshold value is
determined. The third predefined threshold value may be about 0.5.
If the decision is "YES," the ratio is greater than the third
predefined threshold value, and in block 458, the tip 112 is
determined to be in the right atrium. Then, the method 450 ends. If
the decision in decision block 457 is "NO," the ratio is less than
or equal to the third predefined threshold value, and in block 459,
the tip 112 is determined to be in the right ventricle. Then, the
method 450 ends.
Within at least a portion of the range defined between the first
and second threshold values (e.g., about 2.0 to about 8.0), the P
wave voltage measured using prior art techniques, such as those
disclosed by U.S. Pat. Nos. 5,078,678 and 5,121,750 (both issued to
Katims), has generally not yet reached its maximum value.
Therefore, the present method indicates the tip 112 should be
withdrawn before those techniques would signal withdrawal. For
example, typically the P wave voltage within the proximal SVC is
about 0.2 to about 0.3 mV. Near the SA node, the P wave voltage may
increase about 8 fold (e.g., about 1.6 mV to about 2.4 mV. In other
words, the ratio is about 8 near the SA node, which is the location
of the maximum P wave voltage used in the prior art. However, prior
art techniques advise to advance the tip until it can be clearly
seen that the maximum P voltage has been reached. Therefore, the
prior art techniques allow the tip 112 to advance further into the
right atrium than the present technique before identifying the
advancement should be halted and the tip withdrawn back into the
SVC. Because the present technique halts the advancement of the tip
112 earlier (e.g., when the P wave voltage increases above the
second predefined threshold value of about 8.0, which corresponds
to about 1.6 mV to about 2.4 mV) than prior art techniques, the
present teachings may avoid many of the risks associated with
advancing the tip into the right atrium.
Further, the prior art teaches using a threshold percentage
decrease to determine the tip 112 is in the correct location.
However, using a threshold percentage decrease may be ineffective
at locating the tip 112 within the SVC because the percentage
decrease may vary from patient to patient. In other words,
depending upon the anatomical structures of the patient, the tip
112 may have to be withdrawn until the percentage decreases
differing amounts. On the other hand, if the tip 112 is withdrawn
until the ratio is between about 2.0 and about 8.0 (e.g., the
current P wave voltage is about 0.4 mV to about 2.4 mV), the tip
will be located in the mid SVC or in some cases, the distal SVC.
Therefore, the present technique more accurately positions the tip
112 than prior art techniques.
In addition to halting the advancement of the tip 112 when the
ratio of the deflection value of the currently observed P wave to
the reference deflection value has exceeded either of the first and
second predefined threshold values, advancement of the tip 112
could also be halted when the deflection value of the currently
observed P wave is approximately equivalent to the voltage (or
deflection value) of the QRS complex.
As discussed above, when observed using a standard bipolar Lead II
trace, the P wave voltage is almost entirely negative at the top of
the right atrium (see trace 3 of FIG. 2B), biphasic in the mid
right atrium (see trace 4 of FIG. 2B), and positive at the bottom
of the right atrium (see trace 5 of FIG. 2B). A positive/total
deflection ratio may be calculated and used to determine when
advancement of the tip 112 should be halted. The positive/total
deflection ratio is a ratio of the greatest positive deflection
value (of an initial positive or upwardly deflecting portion that
precedes a downwardly deflecting portion) to the total deflection
value of the currently observed P wave. When the positive/total
deflection ratio is greater than a predetermined fraction (e.g.,
one quarter, one eighth, etc.) advancement of the tip 112 should be
halted. For example, the traces 3-5 illustrated in FIG. 2B each
have an initial upwardly deflecting portion. However, in both
cases, the greatest positive deflection value of the initial
upwardly deflecting portion of the P wave is clearly greater than
one quarter of the total deflection value of the currently observed
P wave. As explained above, in these traces, the tip 112 is located
in the right atrium. Thus, if the greatest positive deflection
value is greater than the predetermined fraction of the total
deflection value of the currently observed P wave, the tip 112 is
in the right atrium and should be withdrawn.
Alternate Method of Using a Single Electrode Pair to Determine the
Position of the Tip of the CVC
FIGS. 11A and 11B provide a block diagram of an alternate method
600 of advancing and locating the tip 112 of the CVC 100. A
physical cathode-anode electrode pair is used in a standard bipolar
lead setup. A bipolar lead setup means two physical leads are used
(rather than one virtual lead and one physical lead, which are
referred to as a unipolar lead setup).
For illustrative purposes, the method 600 is described using the
first electrode 114A (see FIG. 3A) functions as a cathode at the
tip 112 and the second electrode 114B (see FIG. 3A) functions as an
anode attached to the patient's skin near his/her right shoulder.
The continuous conductor or column inside the lumen 132, which is
in electrical communication with both the first electrode 114A and
the electrical activity occurring in the environment outside the
tip 112 functions as a "wandering electrode," which is the positive
cathode The second electrode 114B serves as the negative anode
electrode. While technically this configuration is not a standard
Lead II configuration, the trace produced by the electrodes 114A
and 114B may be displayed on a standard ECG monitor using the
monitor's circuitry to display the trace as a bipolar Lead II
trace. Thus, an ECG trace is generated for the wandering electrode
relative to the electrode "RA," which is displayed as a Lead II
trace. However, as is apparent to those of ordinary skill in the
art, through application of ordinary skill in the art to the
present teachings other ECG Lead traces could be used and are
within the scope of the present disclosure.
As is apparent to those of ordinary skill in the art, in a standard
unipolar lead setup, three surface electrodes (not shown) are
attached to a patient's skin: an electrode "RA" is attached to the
patient's right arm (or shoulder), an electrode "LA" is attached to
the patient's left arm (or shoulder), and an electrode "LL" is
attached to the patient's left leg. A virtual electrode may be
created using ECG software, which calculates the virtual electrode
as the electrical center of an Einthoven's triangle created by the
electrodes "RA," "LA," and "LL" used in the Lead I, Lead II, and
Lead III configurations. The continuous conductor or column inside
the lumen 132, which is in electrical communication with both the
first electrode 114A and the electrical activity occurring in the
environment outside the tip 112 functions as a "wandering
electrode." The wandering electrode is the positive cathode, and
the virtual electrode is the negative anode electrode. Thus, an ECG
trace is derived for the wandering electrode relative to the
virtual electrode. In addition to Leads I, II, and III (of the
bipolar configurations), some ECG monitors display unipolar lead
configurations, e.g., aVR, aVL, aVF derived from a composite of the
electrodes "RA," "LA" and "LL," or a chest electrode, variably
called a "V," "MCL," or "Chest" lead (hereafter referred to as the
"V" lead). Some ECG monitors display this ECG trace as a unipolar
"V" lead trace and some users particularly like to use the unipolar
"V" lead trace to guide the tip 112 of the CVC 100. However, most
users use the bipolar Lead II trace generated for the wandering
electrode relative to the electrode "RA" (i.e., the ECG Lead II
configuration discussed above). As is apparent to those of ordinary
skill in the art, with respect to the method 600, any number of
bipolar or unipolar lead configurations may be used with acceptable
results. Further, either the unipolar "V" lead trace or the bipolar
Lead II trace (among others) may be used to perform the method
140.
In method 600, the deflection values measured include only the
negative polarity or downwardly extending portion of the P-wave.
The upwardly extending positive polarity portion is not included in
the measurement of the deflection values. Thus, the deflection
value is calculated as the absolute value of the minimum
deflection.
In first block 610, the CVC 100 is introduced into the venous
system and advanced to an initial location estimated to place the
tip 112 of the CVC 100 at or proximal to the proximal SVC. In next
block 620, a deflection value of the P wave observed at the initial
location is measured and stored as a reference deflection
value.
Then, in block 630, the CVC 100 is advanced from the initial
location to a second location. By way of a non-limiting example,
the CVC 100 may be advanced from the initial location about 0.5 cm
to about 1.0 cm in block 630. At the second location, a new
deflection value is measured using of the P wave observed at the
second location. A deflection ratio of the new deflection value to
the reference deflection value is then calculated. As the method
600 is performed, a maximum deflection ratio observed is stored.
Thus, in block 630, the maximum deflection value observed is equal
to the deflection ratio observed at the second location.
In block 640, the CVC 100 is advanced from the second location by
an incremental distance. By way of a non-limiting example, the
incremental distance may be within a range of about 0.5 cm to about
1.0 cm. However, a smaller sized incremental distance may be used
and is within the scope of the present teachings.
After the CVC 100 has been advanced by the incremental distance, in
block 650, a current deflection value of the P wave observed at the
new location is measured and a current deflection ratio of the
current deflection value to the reference deflection value is
calculated. If the current deflection ratio is greater than the
maximum deflection ratio, the maximum deflection ratio is set equal
to the current deflection ratio. Before the CVC 100 was advanced,
the CVC was located a previous location. The deflection value
measured at the previous location is a previous deflection value
and the deflection ratio of the previous deflection value to the
reference deflection value is a previous deflection ratio.
Then, in decision block 660, the current deflection ratio is
compared to the previous deflection ratio. The decision in decision
block 660 is "YES" when the current deflection ratio is less than
the previous deflection ratio. Otherwise, the decision in decision
block 660 is "NO."
When the decision in decision block 660 is "YES," in block 665, the
CVC 100 is withdrawn from the current location to a new location.
By way of a non-limiting example, in block 665, the CVC 100 may be
withdrawn about 0.5 cm to about 1.0 cm. Then, a new deflection
value of the P wave observed at the new location is measured and a
new deflection ratio of the new deflection value to the reference
deflection value is calculated. If the new deflection ratio is
greater than the maximum deflection ratio, the maximum deflection
ratio is set equal to the new deflection ratio. At this point, the
location of the CVC 100 before withdrawal is a previous location
and the deflection ratio calculated at the previous location is a
previous deflection ratio. The location of the CVC 100 after
withdrawal is a current location and the deflection ratio
calculated at the current location is a current deflection ratio.
By way of a non-limiting example, the CVC 100 may be withdrawn
about 1 cm. Then, the method 600 advances to decision block
670.
In decision block 670 whether the CVC 100 has been withdrawn far
enough is determined. In decision block 670, a positive/total
deflection ratio of the greatest positive deflection value (of an
initial positive or upwardly deflecting portion which precedes a
downwardly deflecting portion) to the total deflection value of the
currently observed P wave is calculated. The decision in decision
block 670 is "YES" when the positive/total deflection ratio is less
than a predetermined fraction (e.g., one quarter, one eighth,
etc.). Otherwise, the decision in decision block 670 is "NO."
Alternatively, in decision block 670, a negative/total deflection
ratio of the smallest negative deflection value (of a negative
polarity or downwardly deflecting portion of the currently observed
P wave which follows an upwardly deflecting positive polarity
portion of the currently observed P wave) to the total deflection
value of the currently observed P wave is calculated. The decision
in decision block 670 is "YES" when the negative/total deflection
ratio is greater than or equal to a predetermined fraction (e.g.,
three quarters, seven eighths, etc.). Otherwise, the decision in
decision block 670 is "NO."
When the decision in decision block 670 is "YES," the method 600
advances to decision block 675. When the decision in decision block
670 is "NO," the method 600 returns to block 665.
In decision block 675, the current deflection ratio is compared to
the maximum deflection ratio observed. The decision in decision
block 675 is "YES" when the current deflection ratio is
approximately equal to the maximum deflection ratio observed. By
way of a non-limiting example, the current deflection ratio may be
considered approximately equal to the maximum deflection ratio
observed when the absolute value of the difference between the
current deflection ratio and the maximum deflection ratio observed
is less than 0.2. If the current deflection ratio is not
approximately equal to the maximum deflection ratio observed, the
decision in decision block 675 is "NO."
When the decision in decision block 675 is "YES," the method 600
ends. When the decision in decision block 675 is "NO," the method
600 returns to block 640
When the decision in decision block 660 is "NO," the current
deflection ratio (calculated after the CVC 100 was advanced by the
current incremental distance) is greater than or equal to the
previous deflection ratio (calculated after the CVC 100 was
advanced by the previous incremental distance). When the decision
in decision block 660 is "NO," the method 600 advances to decision
block 680.
The decision in decision block 680 is "YES," when the current
deflection ratio is less than a maximum threshold value. Otherwise,
decision in decision block 680 is "NO." By way of a non-limiting
example, the maximum threshold value may be about 8.0.
When the decision in decision block 680 is "YES," the current
deflection ratio is less than the maximum threshold value (e.g.,
8.0) and greater than the previous deflection ratio. When this is
the case, the method 600 returns to block 640.
When the decision in decision block 680 is "NO," the current
deflection ratio is greater than or equal to the maximum threshold
value (e.g., 8.0), and the method 600 advances to decision block
685 to determine whether the current deflection ratio is
approximately equal to the maximum threshold value.
When the current deflection ratio is approximately equal to the
maximum threshold value, the decision in decision block 685 is
"YES." Otherwise, decision in decision block 685 is "NO." The
current deflection ratio may be considered approximately equal to
the maximum threshold value when the absolute value of the
difference between the current deflection ratio and the maximum
threshold value is less than 0.2.
When the decision in decision block 685 is "YES," the method 600
ends. When the decision in decision block 685 is "NO," the current
deflection value is neither less than nor equal to the maximum
threshold value. When this occurs, the method 600 progresses to
block 686 whereat the CVC 100 is withdrawn from the current
location to a new location. Then, a new deflection value of the P
wave observed at the new location is measured and a new deflection
ratio of the new deflection value to the reference deflection value
is calculated. The location of the CVC 100 after withdrawal is a
current location and the deflection ratio calculated at the current
location is a current deflection ratio. By way of a non-limiting
example, the CVC 100 may be withdrawn about 1 cm. Then, the method
600 advances to decision block 687.
In decision block 687, the current deflection ratio is compared to
the maximum threshold value. The decision in decision block 670 is
"YES" when the current deflection ratio is approximately equal to
the maximum threshold value. By way of a non-limiting example, the
current deflection ratio may be considered approximately equal to
the maximum threshold value when the absolute value of the
difference between the current deflection ratio and the previous
deflection ratio is less than 0.2. When the current deflection
ratio is not approximately equal to the maximum threshold value,
the decision in decision block 687 is "NO."
When the decision in decision block 687 is "YES," the method 600
ends. When the decision in decision block 670 is "NO," the method
600 advances to decision block 690. Decision block 690 determines
whether the CVC 100 was withdrawn too far in block 686. The
decision in decision block 690 is "YES" when the current deflection
ratio is less than maximum threshold value. When this occurs,
continuing to withdraw the CVC 100 will simply reduce the current
deflection value. Thus, to make the current deflection ratio
approximately equal to the maximum threshold value, the CVC 100
must be advanced.
The decision in decision block 690 is "NO" when the current
deflection ratio is greater than the maximum threshold value. Thus,
to make the current deflection ratio approximately equal to the
maximum threshold value, the CVC 100 must be withdrawn. When the
decision in decision block 690 is "NO," the method 600 returns to
block 686.
If at anytime during the performance of the method 600, the current
deflection ratio is approximately equal to the previously observed
maximum deflection ratio, advancement and withdrawal of the CVC 100
may be halted and performance of the method 600 terminated.
Similarly, if at anytime during the performance of the method 600,
the current deflection ratio is approximately equal to the maximum
threshold value, advancement and withdrawal of the CVC 100 is
halted and performance of the method 600 terminated.
Method of Using a Single Electrode Pair to Determine the Location
of the Tip of the CVC within the Right Atrium
As discussed above, the P wave voltage is almost entirely negative
at the top of the right atrium (see trace 3 of FIG. 2B), biphasic
in the mid right atrium (see trace 4 of FIG. 2B), and positive at
the bottom of the right atrium (see trace 5 of FIG. 2B). Referring
to FIG. 6, a method 190 uses these characteristics of the P wave
voltage to determine the location of the tip 112 of the CVC 100
within the atrium. As is apparent to those of ordinary skill in the
art, with respect to the method 190, either the unipolar "V" lead
trace or the bipolar Lead II trace may be used.
In block 191, any method known in the art or described herein is
used to determine the tip 112 is located in the atrium. For
example, the tip 112 is in the atrium when the ratio of the
deflection value of the currently observed P wave to the reference
deflection value is greater than a value that may vary from person
to person but is within a range of about 4.0 to about 8.0.
Alternatively, the tip 112 may be determined to be in the atrium
when the P wave voltage has exceeded a predetermined amount (e.g.,
about 0.8 mV to about 2.4 mV). Further, the tip 112 may be
determined to be in the atrium when the positive/total deflection
ratio (i.e., a ratio of the greatest positive deflection value of
the initial upwardly deflecting portion of the currently observed P
wave, which precedes a downwardly deflecting portion, to the total
deflection value) is greater than the predetermined fraction (e.g.,
one quarter, one eighth, etc.). By way of another example, the tip
112 may be determined to be in the atrium when the voltage (or
deflection value) of the currently observed P wave is approximately
equivalent to or greater than the voltage (or deflection value) of
the ORS complex.
After it is determined the tip 112 is in the right atrium, in block
192, a positive/negative deflection ratio is calculated. The
positive/negative deflection ratio is a ratio of the greatest
positive deflection value to the smallest negative deflection
value. As discussed above, the absolute value of the deflection
values may used. Thus, the positive/negative deflection ratio may
be calculated as a ratio of the deflection value having the largest
absolute value within the portion of the P wave that has a positive
polarity to the deflection value having the largest absolute value
within the portion of the P wave having a negative polarity. If the
P wave is entirely negative, the positive/negative ratio is zero
(and the tip 112 is in the upper atrium). On the other hand, if the
largest positive deflection value and the smallest negative
deflection value are equal, the positive/negative deflection ratio
is equal to one. In subsequent blocks 193-197, the
positive/negative deflection ratio is used to determine whether the
tip 112 is located in the upper, mid, or lower atrium.
In decision block 193, whether the positive/negative deflection
ratio is less than a first predetermined threshold value is
determined. The first predetermined threshold value may be about
0.80. If decision block 193 determines the ratio is less than the
first predetermined threshold value, in block 194, the method 190
determines the tip 112 is in the upper atrium and the method 190
ends.
If decision block 193 determines the ratio is not less than the
first predetermined threshold value, the method 190 advances to
decision block 195. In decision block 195, whether the
positive/negative deflection ratio is greater than a second
predetermined threshold value is determined. The second
predetermined threshold value may be about 1.20. If decision block
195 determines the ratio is greater than the second predetermined
threshold value, in block 196, the method 190 determines the tip
112 is in the lower atrium and the method 190 ends.
If decision block 195 determines the ratio is not greater than the
second predetermined threshold value, in block 197, the method 190
determines the tip 112 is in the mid atrium and the method 190
ends. In other words, if the positive/negative deflection ratio is
between the first and second predetermined threshold values, the
tip 112 is in the mid atrium. Further, if the positive/negative
deflection ratio is equal to the first predetermined threshold
value or the second predetermined threshold value, the tip 112 is
in the mid atrium.
The following table summarizes the relationship between the
location of the tip 112 of the CVC 100 and the positive/negative
deflection ratio:
TABLE-US-00002 TABLE 2 Location of the tip 112 Upper Mid Lower
Atrium Atrium Atrium Positive/Negative Deflection Ratio: <0.80
0.80-1.20 >1.20 ratio of the greatest positive deflection value
to the smallest negative deflection value
While Table 2 provides exemplary ranges and/or threshold values for
use as a general guideline, those of ordinary skill in the art
appreciate that these values may benefit from adjustment as
additional anatomic or electrophysiologic data is acquired and such
modified values are within the scope of the present invention.
Embodiments Using Two or More Pairs of Electrodes
In the embodiment depicted in FIG. 3B, the CVC 100 includes four
longitudinally spaced apart electrodes 150, 152, 154, and 156. Each
electrode 150, 152, 154, and 156 is in electrical communication
with a wire 160, 162, 164, and 166, respectively. In particular
embodiments, the electrodes 150, 152, 154, and 156 are constructed
from the distal end of each of the wires 160, 162, 164, and 166. In
another embodiment, the electrodes 150, 152, 154, and 156 are
attached to the ends of the wires 160, 162, 164, and 166 by any
method known in the art for attaching an electrode to a wire,
including soldering. The wires 160, 162, 164, and 166 are
electrically isolated from one another. The wires 160, 162, 164,
and 166 may be insulated from the environment outside the body 130
by the body 130.
The electrodes 150, 152, 154, and 156 and the wires 160, 162, 164,
and 166 may be constructed from any suitable materials known in the
art such as stainless steel or platinum. Alternatively, a column of
conductive material such as an electrolytic material (e.g., saline)
may be used to construct one or more of the electrodes 150, 152,
154, and 156 and/or the wires 160, 162, 164, and 166. The
electrodes 150, 152, 154, and 156 may be about 6 mm to about 12 mm
long, about 6 mm to about 12 mm wide, and about 1 mm to about 4 mm
thick. The wires 160, 162, 164, and 166 may be constructed using
any electrical lead wire suitable for obtaining an ECG trace.
Optionally, the invention may include two longitudinally spaced
apart electrodes 157 and 158. Each of the electrodes 157 and 158
may be electrical communication with a wire 167 and 168,
respectively. The electrodes 157 and 158 and wires 167 and 168 may
be constructed in a manner substantially similar to that used to
construct the electrodes 150, 152, 154, and 156 and the wires 160,
162, 164, and 166, respectively. In particular embodiments, the
electrode 157 and 158 are positioned proximal to the electrodes
150, 152, 154, and 156.
Electrodes 150, 152, 154, and 156 may form two anode/cathode pairs.
For example, electrodes 150 and 152 may form a first or proximal
anode/cathode pair 180 and electrodes 154 and 156 may form a second
or distal anode/cathode pair 182. Optional electrodes 157 and 158
may form an optional third or reference anode/cathode pair 184. A
pair of electrodes forming an anode/cathode pair may be attached to
a pair of insulated wires housed within a single cable. In
particular embodiments, a pair of bipolar lead wires are used. In
this manner, the four electrodes of the proximal and distal
anode/cathode pairs 180 and 182 may be attached to two lead wires.
A third bipolar lead wire may be included for use with the
reference anode/cathode pair 184. Alternatively, the proximal and
distal anode/cathode pairs 180 and 182 may be attached to four
insulated wires housed within a single cable such a dual bipolar
lead wire.
The wires 160, 162, 164, and 166 and electrodes 150, 152, 154, and
156 may be permanently embedded into the body 130 of the CVC 100 or
removably inserted into one or more channels or lumens 132 formed
in the CVC 100 for potential future removal and/or replacement. The
wires 167 and 168 and electrodes 157 and 158 may be incorporated
into the CVC 100 in any manner described with respect to wires 160,
162, 164, and 166 and electrodes 150, 152, 154, and 156,
respectively.
The electrodes 150, 152, 154, and 156 are in electrical
communication with the environment outside the CVC 100. In
particular embodiments, a portion of each of the electrodes 150,
152, 154, and 156 are exposed to the environment outside the CVC
100 by apertures 170, 172, 174, and 176 formed in the body 130
adjacent to the electrodes 150, 152, 154, and 156, respectively. In
embodiments including optional electrodes 157 and 158, a portion of
each of the electrodes 157 and 158 may be exposed to the
environment outside the CVC 100 by apertures 177 and 178 formed in
the body 130 adjacent to the electrodes 157 and 158, respectively.
The apertures 177 and 178 may be constructed in any manner suitable
for constructing apertures 170, 172, 174, and 176. The apertures
170, 172, 174, and 176 may be formed in the body 130 by any method
known in the art and the invention is not limited by the method
used to construct the apertures 170, 172, 174, and 176. While the
electrodes 150, 152, 154, and 156 depicted in the drawings extend
outwardly from the body 130 through the apertures 170, 172, 174,
and 176, it is understood by those of ordinary skill in the art,
that electrodes 150, 152, 154, and 156 may reside at the bottom of
the apertures 170, 172, 174, and 176 which may provide a passageway
for fluids in the outside environment to the electrodes 150, 152,
154, and 156. Alternatively, the portion of the electrodes 150,
152, 154, and 156 in electrical communication with the environment
outside the CVC 100 may be flush with the outside surface of the
CVC 100.
The electrode 156 may be located at or spaced from the tip 112. In
particular embodiments, the electrode 156 is less than about 5 mm
from the tip 112. The spacing between an anode and cathode of the
anode/cathode pairs 180 and 182 may be about 1 mm to about 4 mm. In
particular embodiments, the spacing between an anode and cathode of
the anode/cathode pairs 180 and 182 is about 3 mm.
In particular embodiments, the distance between the electrodes 154
and 152 is less than the height of the right atrium. In an adult,
the height of the right atrium may be approximately equal to or
greater than about 4 cm. In one exemplary embodiment, the distance
between the electrode 154 and 152 may be about 3 cm. In embodiments
including optional electrodes 157 and 158, the distance between the
electrodes 150 and 158 may be about 10 cm to about 18 cm.
Those of ordinary skill in the art appreciate that the size and
spacing of the electrodes provided herein may require modification
for use with patients that are larger or smaller than a typical
adult and such embodiments are within the scope of the present
invention. For example, smaller electrodes with a closer spacing
may be required for use with a pediatric patient.
Referring to FIG. 7, the CVC 100 may gain venous access to the SVC
by any method known in the art including inserting the CVC 100 in a
standard sterile fashion through the subclavian, one of the jugular
veins, or a peripheral vein and directing the tip 112 of the CVC
100 through that vein to the SVC.
Each of the anode/cathode pairs 180 and 182 may be used to generate
an ECG trace. In this manner, the ECG waveforms detected by the
proximal pair 180 may be compared to the ECG waveform detected by
the distal pair 182. In particular embodiments, the P wave portion
of each trace is compared to determine the position of the tip 112
of the CVC 100 within the SVC, right atrium, and right
ventricle.
In embodiments including the reference anode/cathode pair 184, the
reference anode/cathode pair 184 may be used to generate an ECG
trace. Referring to FIG. 7, because the reference anode/cathode
pairs 184 may be located substantially proximally from the proximal
and distal anode/cathode pairs 180 and 182, the reference
anode/cathode pair 184 may remain in the venous system proximal to
or in the proximal SVC after the proximal and distal anode/cathode
pairs 180 and 182 have entered the heart. In particular
embodiments, the spacing between the anode/cathode pair 184 and the
proximal pair 180 is large enough to insure the reference
anode/cathode pair 184 remains proximal to or inside the proximal
SVC when the distal anode/cathode pair 182 is inside the right
ventricle. In this manner, the reference anode/cathode pair 184 may
be used to detect the ECG waveform within venous system proximal to
or in the proximal SVC while the catheter is being placed.
The ECG waveforms detected by the proximal anode/cathode pair 180
and/or distal anode/cathode pair 182 may be compared to the ECG
waveform detected by the reference anode/cathode pair 184. In
particular embodiments, the P wave portion of the ECG trace
detected by the proximal anode/cathode pair 180 and/or distal
anode/cathode pair 182 is compared to P wave portion of the ECG
trace detected by the reference anode/cathode pair 184 to determine
whether the tip 112 of the CVC 100 is located within the SVC, right
atrium, or right ventricle.
Methods of Determining the Location of the Tip of the CVC Using Two
or More Electrode Pairs
As is apparent to those of ordinary skill in the art, the methods
140, 450, 190, and 600 described above may be performed using the
CVC 100 with two or three pairs of electrodes. With respect to each
of the methods 140, 450, 190, and 600, the electrode 156 of the
distal anode/cathode pair 182 may be substituted for the first
electrode 114A (see FIG. 3A) and the electrode 154 of the distal
anode/cathode pair 182 may be substituted for the second electrode
114B (see FIG. 3A). By way of another non-limiting example, any one
of the electrodes 156, 154, or 152 may be used as the cathode and
any one of the electrodes 154, 152, or 150 proximal to the one used
as the cathode may be used as the anode. Alternatively, with
respect to each of the methods 140, 450, 190, and 600, one or both
of the distal anode/cathode pair 182 may be substituted for the
first electrode 114A (see FIG. 3A) and one or both of the proximal
anode/cathode pair 180 may be substituted for the second electrode
114B (see FIG. 3A). However, as is appreciated by those of ordinary
skill in the art, it may be desirable to use the distal most
electrode as the cathode.
Referring to FIG. 10, an alternate method 500 of determining the
location of the tip 112 of the CVC 100 using two or three pairs of
electrodes will now be described. With respect to method 500,
unless otherwise indicated, the deflection value is calculated as
the sum of the absolute value of the maximum and minimum
deflections when the maximum and minimum deflections have opposite
polarities. The deflection value is calculated as the larger of the
absolute value of the maximum deflection and the absolute value of
the minimum deflection when the maximum and minimum deflections
have the same polarity.
In first block 510, both the distal anode/cathode pair 182 and the
proximal anode/cathode pair 180 are located in the venous system
proximal to or in the proximal SVC. A D/P ratio of the deflection
value of the distal anode/cathode pair 182 to the deflection value
of the proximal anode/cathode pair 180 may be calculated and used
to verify the locations of the distal anode/cathode pair 182 and
the proximal anode/cathode pair 180 within the venous system
proximal to or in the proximal SVC. When both of the anode/cathode
pairs 180 and 182 are within the venous system proximal to or in
the proximal SVC, the deflection value of the P wave detected by
each of them is substantially identical and the D/P ratio of their
P wave deflection values equals approximately one. Optionally, the
deflection value of one or both of the P waves may be stored or
otherwise recorded. For example, the deflection value of the P wave
detected by the distal anode/cathode pair 182 or the proximal
anode/cathode pair 180 may be stored as a reference deflection
value.
In next block 518, the user advances the CVC 100. By way of a
non-limiting example, the user may advance the CVC 100 about 0.5 cm
to about 1.0 cm. Then, in block 520, the D/P ratio of the
deflection value of the distal anode/cathode pair 182 to the
deflection value of the proximal anode/cathode pair 180 is
calculated. Optionally, the deflection value of one or both of the
P waves may be stored or otherwise recorded. Then, the method 500
advances to decision block 524.
The user or operator may wish to continue advancing the CVC 100
until the SA node is detected. When an anode/cathode pair 180 or
182 is approximately 4 cm proximal to the SA node and therefore, by
inference, approximately 4 cm proximal to the entrance of the right
atrium (or "caval-atrial junction," which is the location of the SA
node), the deflection value of the P wave detected by that
anode/cathode pair may increase.
When the distal anode/cathode pair 182 enters the right atrium and
the proximal anode/cathode pair 180 is still in the venous system
proximal to or in the proximal SVC, the deflection value of the P
wave detected by the distal anode/cathode pair 182 may be at least
four times the deflection value of the P wave detected by the
proximal anode/cathode pair 180. Therefore, when the D/P ratio of
the P wave deflection values of the distal anode/cathode pair 182
to the proximal anode/cathode pair 180 is greater than or equal to
about 4.0 to about 8.0, the user or operator should withdraw the
CVC 100. By way of a non-limiting example, the user may withdraw
the CVC 100 about 0.5 cm to about 1.0 cm.
In decision block 524, a predetermined maximum threshold value
"TR1" may be used to determine whether the user or operator should
withdraw the CVC 100. If the D/P ratio exceeds the maximum
threshold value "TR1," the decision in decision block 524 is "YES,"
and in block 528, the CVC 100 is withdrawn. In particular
embodiments, the maximum threshold value "TR1" may range from
approximately 4.0 to approximately 8.0. By way of a non-limiting
example, the maximum threshold value "TR1" may be about 8.0. If the
D/P ratio does not exceed the maximum threshold value "TR1," the
decision in decision block 524 is "NO," and the method 500 advances
to decision block 532.
When the distal anode/cathode pair 182 enters the right ventricle,
the proximal anode/cathode pair 180 may be in the right atrium.
Because the deflection value of the P wave experienced in the right
ventricle is approximately equal to the deflection value of the P
wave experienced in the proximal SVC, the D/P ratio of the P wave
deflection values of the distal anode/cathode pair 182 to the
proximal anode/cathode pair 180 (which is now in the upper atrium)
is less than or equal to about one half. Therefore, when the D/P
ratio is less than about one half, the user or operator should
withdraw the CVC 100.
In decision block 532, a predetermined minimum threshold value
"TMIN" may be used to determine whether the user or operator should
withdraw the CVC 100, If the D/P ratio is less than the
predetermined minimum threshold value "TMIN," the decision in
decision block 532 is "YES," and in block 528, the CVC 100 is
withdrawn. In particular embodiments, the predetermined minimum
threshold value "TMIN" may be approximately one half.
If the D/P ratio is not less than the minimum threshold value
"TMIN," the decision in decision block 532 is "NO," and the distal
anode/cathode pair 182 and the proximal anode/cathode pair 180 may
both be in the right atrium at the same time. When this occurs, the
deflection value of the P waves detected by each would be very
similar if not identical making their D/P ratio approximately equal
to one. Therefore, in block 536, a P/R ratio or D/R ratio
(described below) may be calculated to determine the location of
the tip 112 of the CVC 100.
The P/R ratio may include the ratio of the deflection value of the
P wave detected by the proximal anode/cathode pair 180 to the
stored reference deflection value of the P wave detected in the
proximal SVC. In particular embodiments, the P/R ratio may include
the ratio of the deflection value of the P wave detected by the
proximal anode/cathode pair 180 to a reference deflection value of
the P wave detected by the reference anode/cathode pair 184. In
embodiments that include a reference anode/cathode pair 184, the
reference anode/cathode pair 184 may be used to detect the P wave
in the proximal SVC. Because the proximal anode/cathode pair 180 is
inside the right atrium, the deflection value of its P wave is
greater than or equal to about four times to about eight times the
deflection value of the P wave observed in the proximal SVC. When
the P/R ratio is equal to or greater than a threshold value "TR2"
within a range of about 4.0 to about 8.0, the user or operator
should withdraw the CVC 100. By way of a non-limiting example, the
threshold value "TR2" may be about 4.0. By way of a non-limiting
example, the threshold value "TR2" may be equal to the
predetermined maximum threshold value "TR1." Alternatively, the
threshold value "TR2" could be set equal the largest D/R ratio
observed thus far.
After the P/R ratio is calculated, in decision block 540, the
threshold value "TR2" may be used to determine whether the user or
operator should withdraw the CVC 100. If the P/R ratio exceeds the
threshold value "TR2," the decision in decision block 540 is "YES,"
and in block 528, the CVC 100 is withdrawn. Otherwise, if the P/R
ratio does not exceed the threshold value "TR2," the user does not
need to withdraw the CVC 100, and the decision in decision block
540 is "NO." Then, the method 500 ends.
Alternatively, in block 536, a D/R ratio may be calculated to
determine the location of the tip 112 of the CVC 100. The D/R ratio
may include the ratio of the deflection value of the P wave
detected by the distal anode/cathode pair 182 to the stored
reference deflection value of the P wave detected in the proximal
SVC. In particular embodiments, the D/R ratio may include the ratio
of the deflection value of the P wave detected by the distal
anode/cathode pair 182 to the reference deflection value of the P
wave detected by the reference anode/cathode pair 184. In
embodiments that include a reference pair 184, the reference pair
184 may be used to detect the P wave in the proximal SVC. Because
the distal anode/cathode pair 182 is inside the right atrium, the
deflection value of its P wave is greater than or equal to about
four times to about eight times the deflection value of the P wave
observed in the proximal SVC.
When D/R ratio is equal to or greater than a threshold value "TR3"
within a range of about 4.0 to about 8.0, the user or operator
should withdraw the CVC 100. By way of a non-limiting example, the
threshold value "TR3" may be about 4.0. By way of a non-limiting
example, the threshold value "TR3" may be equal to the
predetermined maximum threshold value "TR1." Alternatively, the
threshold value "TR3" could be set equal the largest D/R ratio
observed thus far. Under these circumstances, in decision block
540, the threshold value "TR3" may be used to determine whether the
user or operator should withdraw the CVC 100, i.e., if the D/R
ratio exceeds the threshold value "TR3," the decision in decision
block 540 is "YES," and the CVC 100 is withdrawn in block 528.
Otherwise, if the D/R ratio does not exceed the threshold value
"TR3," the user does not need to withdraw the CVC 100, and the
decision in decision block 540 is "NO." Then, the method 500
ends.
After the CVC 100 is withdrawn in block 528, the method 500 may
return to block 520 to recalculate the D/P ratio.
In method 500, determining when to withdraw the CVC 100 is
unaffected by wide anatomic variability between individual people
because instead of using predetermined threshold deflection values,
the D/P ratio, P/R ratio, and/or D/R ratio of deflection values
obtained from each individual is used.
The following table summarizes the relationship between the
location of the tip 112 of the CVC 100 and the deflection values of
the P waves detected by the proximal and distal anode/cathode pairs
180 and 182:
TABLE-US-00003 TABLE 3 Location of the distal Proximal Right Right
Right anode/cathode pair 182 SVC Atrium Atrium Ventricle Location
of the proximal Proximal Proximal Right Right anode/cathode pair
180 SVC SVC Atrium Atrium D/P ratio: Ratio of the deflec-
.apprxeq.1 .gtoreq.TR1 .apprxeq.1 .ltoreq.TMIN tion value of the
distal anode/ cathode pair 182 to the de- flection value of the
proximal anode/cathode pair 180 P/R ratio: Ratio of the deflec-
.apprxeq.1 .apprxeq.1 .gtoreq.TR2 .gtoreq.TR2 tion value of the P
wave de- tected by the proximal anode/ cathode pair 180 and the de-
flection value of the P wave detected in the proximal SVC D/R
ratio: Ratio of the deflec- .apprxeq.1 .gtoreq.TR3 .gtoreq.TR3
.apprxeq.1 tion value of the P wave de- tected by the distal anode/
cathode pair 182 and the de- flection value of the P wave detected
in the proximal SVC
As mentioned above, each of the threshold values "TR1," "TR2," and
"TR3" in Table 3 may be within a range of about 4.0 to about 8.0
and the minimum threshold value "TMIN" may be about 0.5.
Alternatively, the threshold values "TR1," "TR2," and "TR3" in
Table 3 may be set equal the largest D/R ratio observed during the
performance of the method 500. By way of another example, the
threshold values "TR1," "TR2," and "TR3" in Table 3 may be set
equal the largest D/R ratio observed for the patient during the
performance of any of the methods described herein and recorded for
use with the method 500. While exemplary threshold values "TR1,"
"TR2," "TR3," and "TMIN" have been provided for use as a general
guideline, those of ordinary skill in the art appreciate that these
values may benefit from adjustment as additional anatomic or
electrophysiologic data is acquired and such modified values are
within the scope of the present invention.
As is apparent from Table 3, either of the P/R ratio and the D/R
ratio may be calculated first and used instead of the D/P ratio.
For example, if the P/R ratio is calculated first, it may be
compared to the threshold value "TR2." If the P/R ratio is greater
than or equal to the threshold value "TR2," the tip 112 is in the
right atrium or right ventricle and should be withdrawn. If the P/R
ratio is less than the threshold value "TR2," the tip 112 is in the
right atrium or proximal SVC. When this occurs, either the D/P
ratio or the D/R ratio may be calculated. If the D/P ratio is
calculated, it may be compared to the predetermined maximum
threshold value "TR1." If the D/P ratio is greater than or equal to
the predetermined maximum threshold value "TR1," the tip 112 should
be withdrawn. If the D/R ratio is calculated, it may be compared to
the threshold value "TR3." If the D/R ratio is greater than or
equal to the threshold value "TR3," the tip 112 should be
withdrawn.
Alternatively, if the D/R ratio is calculated first, it may be
compared to the threshold value "TR3." If the D/R ratio is greater
than or equal to the threshold value "TR3," the tip 112 is in the
right atrium and should be withdrawn. If the D/R ratio is less than
the threshold value "TR3," the tip 112 is in the right ventricle or
proximal SVC. When this occurs, either the D/P ratio or the P/R
ratio may be calculated. If the D/P ratio is calculated, it may be
compared to the predetermined minimum threshold value "TMIN." If
the D/P ratio is less than or equal to the predetermined minimum
threshold value "TMIN," the tip 112 should be withdrawn. If the P/R
ratio is calculated, it may be compared to the threshold value
"TR2." If the P/R ratio is greater than or equal to the threshold
value "T<2," the tip 112 should be withdrawn.
In addition to using the method 500 to determine when to withdraw
the CVC 100, the QRS complex portion of the ECG waveforms detected
by the distal anode/cathode pair 182 and/or the proximal
anode/cathode pair 180 may be used to determine when the tip 112 of
the CVC 100 is in the right atrium. Specifically, the tip 112
should be withdrawn because it is in the right atrium when the
deflection value of the P wave detected by either the distal
anode/cathode pair 182 or the proximal anode/cathode pair 180 is
approximately equivalent to or greater than the voltage (or
deflection value) of the QRS complex detected simultaneously by the
same anode/cathode pair. The P wave and QRS complex typically look
similar and deflect in the same direction. The CVC 100 may be
advanced until the deflection value of the P wave is slightly less
than or approximately equal to the deflection value of the QRS
complex.
Further, a positive/total deflection ratio of the largest positive
deflection value (of an initial positive or upwardly deflecting
portion preceding a downwardly deflecting portion of a P wave
detected by the distal anode/cathode pair 182 and/or the proximal
anode/cathode pair 180) to the total deflection value (of the P
wave detected by the distal anode/cathode pair 182 and/or the
proximal anode/cathode pair 180) may be used to determine when the
tip 112 of the CVC 100 is in the right atrium. As discussed above,
the P wave voltage is almost entirely negative at the top of the
right atrium (see trace 3 of FIG. 2B), biphasic in the mid right
atrium (see trace 4 of FIG. 28), and positive at the bottom of the
right atrium (see trace 5 of FIG. 2B). Thus, advancement of the tip
112 may be halted when the positive/total deflection ratio is
greater than a predetermined fraction (e.g., one quarter, one
eighth, etc.). As mentioned above, with respect to the single
electrode pair embodiments, when the positive/total deflection
ratio exceeds the predetermined fraction, the tip 112 is in the
right atrium.
As is apparent to those of ordinary skill, the proximal and distal
anode/cathode pairs 180 and 182 may be used to detect the
instantaneous location of the tip 112. Therefore, if the tip 112
migrates into the atrium or ventricle, this movement may be
detected immediately. Following such an occurrence, a medical
professional may be alerted via a signal, such as an alarm, and the
like, to reposition the tip 112.
If the tip 112 is determined to be in the atrium, the method 190
described above may be used to determine the position of the tip
112 inside the atrium. Specifically, the electrode 114B (see FIG.
3A) may be attached to the skin of the patient. Then, the method
190 may be used to determine a positive/negative deflection ratio
for the P wave detected by the electrode 114B and one of the
electrodes 154 and 156 of the distal anode/cathode pair 182. The
positive/negative deflection ratio may be compared to the first and
second threshold values (see Table 2) and the location of the tip
112 within the atrium determined. Alternatively, instead of
attaching the electrode 114B to the skin of the patient, one of the
electrodes 157 and 158 of the reference anode/cathode pair 184 may
be used. In such embodiments, the positive/negative deflection
ratio is determined for the P wave detected by one of the
electrodes 157 and 158 of the reference anode/cathode pair 184 and
one of the electrodes 154 and 156 of the distal anode/cathode pair
182. As mentioned above, it may desirable to use the most distal
electrode 156 of the distal anode/cathode pair 182. The
positive/negative deflection ratio may be compared to the first and
second threshold values (see Table 2) and the location of the tip
112 within the atrium determined.
Because the voltage across each of the anode/cathode pairs 180 and
182 may vary depending over time, the voltage across wires 164 and
166 and wires 160 and 162 may each constitute a time-varying signal
that can be analyzed using standard signal processing methods well
known in the art. In a typical patient, the maximum of voltage
across the anode/cathode pairs 180 and 182 may range from about 0.2
mV to about 3 mV. The signal from each anode/cathode pairs 180 and
182 may be amplified and/or filtered to improve the signal quality.
A distal signal may be detected by the distal anode/cathode pair
182 and a proximal signal may be detected by the proximal
anode/cathode pair 180. Similarly, an optional reference signal may
be detected by the reference anode/cathode pair 184.
A separate ECG trace may be constructed for distal and proximal
signals. In some embodiments, an ECG trace may also be constructed
for the reference signal. The P wave portion of one or more of
these ECG traces may be identified and analyzed. For example, the
ECG trace of the distal signal may be visualized by connecting
wires 164 and 166 of the distal anode/cathode pair 182 to a device
such as a PACERVIEW.RTM. signal conditioner designed specifically
to construct and display an ECG trace from a time varying low
voltage signal. Similarly, the ECG trace of the proximal signal may
be viewed by connecting the wires 160 and 162 of the proximal
anode/cathode pair 180 to a PACERVIEW.RTM. signal conditioner. The
ECG trace of the reference signal may be viewed by connecting the
wires 167 and 168 of the proximal anode/cathode pair 184 to a
PACERVIEW.RTM. signal conditioner.
In particular embodiments, each of the four wires 160, 162, 164,
and 166 may be coupled to a signal analysis system for analysis of
the voltage information detected by the electrodes 150, 152, 154,
and 156, respectively. In embodiments including electrodes 157 and
158, the wires 167 and 168 may be coupled to the signal analysis
system for analysis of the voltage information detected by the
electrodes 157 and 158, respectively. An exemplary signal analysis
system 200 for analyzing the signals carried by wires 160, 162,
164, and 166 and alerting the user or operator when to withdraw the
tip 112 of the CVC 100 may be viewed in FIG. 7. In an alternate
embodiment, the system 200 may also analyze the signals carried by
wires 167 and 168.
System 200
FIG. 8 is a block diagram of the components of the exemplary system
200. The system 200 may include a programmable central processing
unit (CPU) 210 which may be implemented by any known technology,
such as a microprocessor, microcontroller, application-specific
integrated circuit (ASIC), digital signal processor (DSP), or the
like. The CPU 200 may be integrated into an electrical circuit,
such as a conventional circuit board, that supplies power to the
CPU 210. The CPU 210 may include internal memory or memory 220 may
be coupled thereto. The memory 220 may be coupled to the CPU 210 by
an internal bus 264.
The memory 220 may comprise random access memory (RAM) and
read-only memory (ROM). The memory 220 contains instructions and
data that control the operation of the CPU 210. The memory 220 may
also include a basic input/output system (BIOS), which contains the
basic routines that help transfer information between elements
within the system 200. The present invention is not limited by the
specific hardware component(s) used to implement the CPU 210 or
memory 220 components of the system 200.
All or a portion of the deflection values and/or deflection ratios
calculated by the methods 140, 190, 450, 500, and 600, including
the reference deflection value, may be stored in the memory 220 for
use by the methods.
Optionally, the memory 220 may include external or removable memory
devices such as floppy disk drives and optical storage devices
(e.g., CD-ROM, R/W CD-ROM, DVD, and the like). The system 200 may
also include one or more I/O interfaces (not shown) such as a
serial interface (e.g., RS-232, RS-432, and the like), an IEEE-488
interface, a universal serial bus (USB) interface, a parallel
interface, and the like, for the communication with removable
memory devices such as flash memory drives, external floppy disk
drives, and the like.
The system 200 may also include a user interface 240 such as a
standard computer monitor, LCD, colored lights 242 (see FIG. 7),
PACERVIEW.RTM. signal conditioner, ECG trace display device 244
(see FIG. 7), or other visual display including a bedside display.
In particular embodiments, a monitor or handheld LCD display may
provide an image of a heart and a visual representation of the
estimated location of the tip 112 of the CVC 100. The user
interface 240 may also include an audio system capable of playing
an audible signal. In particular embodiments, the user interface
240 includes a red light indicating the CVC 100 should be withdrawn
and a green light indicating the CVC 100 may be advanced. In
another embodiment, the user interface 240 includes an ECG trace
display device 244 capable of displaying the ECG trace of the
distal and proximal signals. In the embodiment depicted in FIG. 7,
the user interface 240 includes a pair of lights 242, one red and
the other green, connected in series with a ECG trace display
device 244. In some embodiments, a display driver may provide an
interface between the CPU 210 and the user interface 240. Because
an ultrasound machine is typically used when placing peripherally
inserted central catheters ("PICC" lines), the system 200 may be
incorporated into an ultrasound unit (not shown).
The user interface 240 may permit the user to enter control
commands into the system 200. For example, the user may command the
system 200 to store information such as the deflection value of the
P wave inside the SVC. The user may also use the user interface 240
to identify which portion of the ECG trace corresponds to the P
wave. The user interface 240 may also allow the user or operator to
enter patient information and/or annotate the data displayed by
user interface 240 and/or stored in memory 220 by the CPU 210. The
user interface 240 may include a standard keyboard, mouse, track
ball, buttons, touch sensitive screen, wireless user input device
and the like. The user interface 240 may be coupled to the CPU 210
by an internal bus 268.
Optionally, the system 200 may also include an antenna or other
signal receiving device (not shown) such as an optical sensor for
receiving a command signal such as a radio frequency (RF) or
optical signal from a wireless user interface device such as a
remote control. The system 200 may also include software components
for interpreting the command signal and executing control commands
included in the command signal. These software components may be
stored in memory 220.
The system 200 includes an input signal interface 250 for receiving
the distal and proximal signals. The input signal interface 250 may
also be configured to receive the reference signal. The input
signal interface 250 may include any standard electrical interface
known in the art for connecting a double dipole lead wire to a
conventional circuit board as well as any components capable of
communicating a low voltage time varying signal from a pair of
wires through an internal bus 262 to the CPU 210. The input signal
interface 250 may include hardware components such as memory as
well as standard signal processing components such as an analog to
digital converter, amplifiers, filters, and the like.
The various components of the system 200 may be coupled together by
the internal buses 262, 264, and 268. Each of the internal buses
262, 264, and 268 may be constructed using a data bus, control bus,
power bus, I/O bus, and the like.
The system 200 may include instructions 300 executable by the CPU
210 for processing and/or analyzing the distal and/or proximal
signals. These instructions may include computer readable software
components or modules stored in the memory 220. In particular
embodiments, the instructions 300 include instructions for
performing the method 500 (see FIG. 10).
The instructions 300 may include an ECG Trace Generator Module 310
that generates a traditional ECG trace from the distal and/or
proximal signals. In some embodiments, the ECG Trace Generator
Module 310 may generate a traditional ECG trace from the reference
signal. As is appreciated by those of ordinary skill in the art,
generating an ECG trace from an analog signal, such as the distal
and proximal signals, may require digital or analog hardware
components, such as an analog to digital converter, amplifiers,
filters, and the like and such embodiments are within the scope of
the present invention. In particular embodiments, some or all of
these components may be included in the input signal interface 250.
In an alternate embodiment, some or all of these components may be
implemented by software instructions included in the ECG Trace
Generator Module 310. The ECG Trace Generator 310 may include any
method known in the art for generating an ECG trace from a time
varying voltage signal.
The ECG Trace Generator 310 may record one or more of the ECG
traces generated. Presently, a chest x-ray is used to document the
location of the tip 112. This documentation may be used to prove
the tip 112 of the CVC was placed correctly. Using the present
techniques, the recorded ECG trace(s) may be used in addition to or
instead of the chest x-ray to document tip 112 location. For
example, the recorded ECG trace(s) may demonstrate that the tip 112
has migrated from the proximal SVC into the right atrium. Further,
the recorded ECG trace(s) could document the repositioning of the
tip 112 back into proximal SVC. Additionally, the recorded ECG
trace(s) could document that the tip 112 was initially placed
correctly and did not migrate from its initial position. In this
manner, the ECG trace(s) could be used to document the correct or
incorrect placement of the tip 112 and could be included in the
patient's medical record, replacing or supplementing the prior art
chest x-ray. Further, if the tip 112 does migrate, the recorded ECG
trace(s) could be used to determine whether the tip entered the
atrium, how far into the atrium the tip migrated, and/or whether
the tip entered the ventricle.
The instructions 300 may include a P Wave Detection Module 320 for
detecting or identifying the P wave portion of the ECG trace. The P
wave portion of the ECG trace may be detected using any method
known in the art. In particular embodiments, the P Wave Detection
Module 320 receives input from the user or operator via the user
interface 240. The input received may identify the P wave portion
of the ECG trace. Optionally, the P Wave Detection Module 320 may
include instructions for identifying the QRS complex as well as the
P wave portion of the ECG trace. Further, the P Wave Detection
Module 320 may include instructions for determining a deflection
value for an initial upwardly deflecting portion of a single P wave
preceding a downwardly deflecting portion. The P Wave Detection
Module 320 may also include instructions for determining a
positive/total deflection ratio of the largest positive deflection
value for the initial upwardly deflecting portion of the P wave to
the deflection value for the entire P wave.
The instructions 300 may include an Interpretive Module 330 for
comparing the P wave generated for the distal, proximal, and/or
reference signals. In particular embodiments, the Interpretive
Module 330 determines the deflection value of the P wave generated
for the distal and/or proximal signals. In some embodiments, the
Interpretive Module 330 determines the deflection value of the P
wave generated for the reference signal. The Interpretive Module
330 may direct the CPU 210 to store the deflection value of the
distal, proximal, and/or reference signals in memory 220. In
particular, it may be desirable to store the deflection value of
the P wave encountered in the proximal SVC. The Interpretive Module
330 may receive input from the user or operator via the user
interface 240 instructing the Interpretive Module 330 to store the
deflection value. This information could be stored under a unique
patient identifier such as a medical record number so that tip
location information could be accessed anytime during the life of
the CVC 100, potentially avoiding the need for a chest x-ray to
document current location.
With respect to performing the method 500 illustrated in FIG. 10,
the Interpretive Module 330 may also determine the D/P ratio by
calculating the ratio of the deflection value of the distal signal
to the deflection value of the proximal signal. If the D/P ratio is
approximately equal to or greater than the maximum threshold value
"TR1," the tip 112 of the CVC 100 may be in the right atrium. The
Interpretive Module 330 may alert the user or operator that the tip
112 is in the right atrium and the CVC 100 should be withdrawn from
the right atrium. On the other hand, if the D/P ratio is
approximately equal to or less than the minimum threshold value
"TMIN," the tip 112 of the CVC 100 may be in the right ventricle.
The Interpretive Module 330 may alert the user or operator that the
tip 112 is in the right ventricle and the CVC 100 should be
withdrawn therefrom.
If the D/P ratio is less than the maximum threshold value "TR1" and
greater than the minimum threshold value "TMIN," the tip 112 may be
in either the right atrium or the proximal SVC. When this happens,
the Interpretive Module 330 may calculate the P/R ratio and/or the
D/R ratio. For example, if the D/R ratio is approximately equal to
or greater than the threshold value "TR3," the tip may be in the
right atrium and should be withdrawn therefrom. When this occurs,
the Interpretive Module 330 may alert the user or operator that the
tip 112 is in the right atrium. If the D/R ratio is approximately
less than the threshold value "TR3," the tip 112 is in the SVC and
may be advanced if the operator so chooses. The Interpretive Module
330 may communicate to the user or operator that the tip 112 may be
advanced.
On the other hand, if the P/R ratio is approximately equal to or
greater than the threshold value "TR2," the tip may be in the right
atrium or right ventricle and should be withdrawn therefrom. When
this occurs, the Interpretive Module 330 may alert the user or
operator to withdraw the tip 112. If the P/R ratio is approximately
less than the threshold value "TR2," the tip 112 is in the SVC
(because the D/P ratio is less than the maximum threshold value
"TR1") and may be advanced if the operator so chooses. The
Interpretive Module 330 may communicate to the user or operator
that the tip 112 may be advanced.
In an alternate embodiment, the P/R ratio is used instead of the
D/P ratio. Whenever the P/R ratio is approximately equal to or
greater than the threshold value "TR2," the user or operator may be
alerted to withdraw the CVC 100. If the P/R ratio is approximately
less than the threshold value "TR2," the D/P ratio or D/R ratio may
be calculated and used to determine the position of the tip 112 of
the CVC 100.
In another alternate embodiment, the D/R ratio is used instead of
the D/P ratio. Whenever the D/R ratio is approximately equal to or
greater than the threshold value "TR3," the user or operator may be
alerted to withdraw the CVC 100. If the D/R ratio is approximately
less than the threshold value "TR3," the D/R ratio or P/R ratio may
be calculated and used to determine the position of the tip 112 of
the CVC 100.
In particular embodiments, the instructions in the Interpretive
Module 330 direct the CPU 210 to use the user interface 240 to
communicate whether the tip 112 should be withdrawn to the user.
The CPU 210 may use the user interface 240 to communicate the tip
112 may be advanced. Because the Interpretive Module 330 may
interpret the P wave to obtain the deflection values of the distal
and proximal signals, compare the deflection values, and provide
the operator with immediate real-time feedback, the operator need
not interpret the actual ECG waveforms.
Monitor 127
The monitor 127 of the system 121 for use with single pair of
electrode embodiments will now be described. Returning to FIG. 3A,
for illustrative purposes, the monitor 127 is described as coupled
to each of the electrodes 114A and 114B by wires 123 and 129,
respectively. However, in alternate embodiments, the monitor 127 is
coupled to the electrodes 176 and 174 of the distal anode/cathode
pair 182 (see FIG. 3B) by wires 123 and 129, respectively. By way
of another alternate embodiment, one or both of the distal
anode/cathode pair 182 may be coupled to the monitor 127 by wire
123 and one or both of the proximal anode/cathode pair 180 may be
may be coupled to the monitor 127 by wire 129.
Referring to FIG. 9, the monitor 127 includes a signal analysis
system 400 that may be substantially similar to the signal analysis
system 200 described above. Specifically, the system 400 may
construct an ECG trace for the electrical signals detected by the
pair of electrodes 114, and identify and analyze the P wave portion
of the ECG trace using any method discussed above with respect to
the system 200. Further, the system 400 is configured to display
information to the user or operator communicating the current
position of the tip 112 of the CVC 100.
Like reference numerals are used to identify substantially
identical components in FIGS. 8 and 9. The system 400 includes the
CPU 210, the memory 220, the input signal interface 250 for
receiving the signals detected by the pair of electrodes 114, and a
user interface 410. Like system 200, the various components of the
system 400 may be coupled together by the internal buses 262, 264,
and 268.
All or a portion of the deflection values and/or deflection ratios
calculated by the methods 140, 190, 450, and 600, including the
reference deflection value, may be stored in the memory 220 for use
by the methods.
The system 400 differs from the system 200 with respect to the user
interface 410 and at least a portion of the computer-executable
instructions stored in memory 220. Returning to FIG. 3A, in some
embodiments, the user interface 410 includes an array of lights
412, a first portion 412A of which corresponds to ratio values
below or equal to the first predefined threshold value of the
method 140 (see FIG. 4), a second portion 412B of which corresponds
to the range of ratio values greater than the first predefined
threshold value and less than or equal to the second threshold
value of the method 140, and a third portion 412C of which
indicates the second predefined threshold value has been
exceeded.
By way of a non-limiting example, the first portion 412A may
include an array of green lights. The number of green lights lit
may indicate the magnitude of the ratio of the deflection value of
the currently observed P wave to the reference deflection value.
For example, the first portion may include eight lights. The first
light may indicate the ratio is less than or equal to 0.8. For each
0.2 increase in the ratio, another green light may be lit until all
eight green lights are lit and the ratio is approximately equal to
4.0. If the ratio decreases to less than 4.0, for each 0.2 decrease
in the ratio, a green light may be turned off until only a single
green light is lit.
By way of a non-limiting example, the second portion of lights may
include an array of yellow lights. The number of yellow lights lit
may indicate the magnitude of the ratio of the deflection value of
the currently observed P wave to the reference deflection value.
For example, the second portion may include eight yellow lights.
The first yellow light may indicate the ratio is approximately
equal to about 4.4 to about 45. For each 0.2 increase in the ratio
above 4.4, another yellow light may be lit until all eight yellow
lights are lit and the ratio is approximately equal to 6.0. If the
ratio decreases to less than 6.0, for each 0.2 decrease in the
ratio, a yellow light may be turned off until the ratio is less
than 4.4 and none of the yellow lights are lit.
By way of a non-limiting example, the third portion may include a
single red light indicating the magnitude of the ratio of the
deflection value of the currently observed P wave to the reference
deflection value has exceeded 6.0. If the ratio decreases to less
than 6.0, the red light may be turned off. In this manner, the user
interface 410 provides greater resolution for ratio values less
than or equal to the first predefined threshold value than for
ratio values between the first and second predefined threshold
values.
While the above example has been described as including lights
(such as LEDs, conventional light bulbs, and the like), those of
ordinary skill in the art appreciate that any indicator may used
and such embodiments are within the scope of the present teachings.
For example, a monitor displaying a graphical representation of
lights, a figure, such as a bar, that increases or decreases in
size to reflect an increase or decrease in the ratio, and the like
may be used in place of the array of lights. Optionally, the user
interface 410 may include a screen 420 (see FIG. 3A) configured to
display information to the user or operator. For example, the
screen 420 may display an image of a heart and a visual
representation of the estimated location of the tip 112 of the CVC
100. Alternatively, the screen 420 may display the words "ADVANCE,"
"HOLD," or "WITHDRAW" as appropriate.
The user interface 410 may also indicate when the tip 112 is
located in the ventricle. By way of a non-limiting example, the
user interface 410 may include a light, audio signal, or other
indicator configured to indicate the tip 112 has entered the
ventricle.
In some embodiments, a display driver may provide an interface
between the CPU 210 and the user interface 410. Optionally, the
user interface 410 includes an audio system capable of playing an
audible signal. For example, the audio system may produce a tone
that increases in pitch as the ratio increases and decreases in
pitch as the ratio decreases may be used. Alternatively, the audio
system may produce one tone when the ratio is greater than the
first predefined threshold value, indicating the tip 112 should be
withdrawn. In such embodiments, the audio system may produce
another more urgent or annoying tone when the ratio is above the
second predefined threshold value. Further, the audio system may be
silent when the ratio is below the first predefined threshold
value.
The user interface 410 may permit the user to enter control
commands into the system 200. For example, the user may command the
system 200 to store information such as the deflection value of the
P wave inside the proximal SVC (e.g., the reference deflection
value), atrium (e.g., the reference atrium deflection value), and
the like. The user may also use the user interface 410 to identify
manually which portion of the ECG trace corresponds to the P wave.
The user interface 410 may also allow the user or operator to enter
patient information (such as a patient identifier number) and/or
annotate the data displayed by user interface 410 and/or stored in
memory 220 by the CPU 210. The user interface 410 may include a
standard keyboard, mouse, track ball, buttons 416, touch sensitive
screen, wireless user input device and the like. The user interface
410 may be coupled to the CPU 210 by an internal bus 268.
By way of a non-limiting example, a patient's reference deflection
value (detected when the tip 112 was located in the proximal SVC)
and/or reference atrium deflection value (detected when the tip 112
was located in the atrium) could be stored in the memory 220 and
associated with the patient's patient identifier number or some
other identification number. In this manner, the patient's recorded
reference deflection value could be used anytime during the life of
the CVC 100 by recalling the reference deflection value from memory
220 using the patient's patient identifier number, which could be
entered manually using the user interface 410.
Optionally, the system 400 may also include an antenna or other
signal receiving device (not shown) such as an optical sensor for
receiving a command signal such as a radio frequency (RF) or
optical signal from a wireless user interface device such as a
remote control. The system 400 may also include software components
for interpreting the command signal and executing control commands
included in the command signal. These software components may be
stored in memory 220.
The system 400 includes instructions 300 executable by the CPU 210
for processing and/or analyzing the electrical signals detected by
the pair of electrodes 114. The instructions 300 may include the
ECG Trace Generator Module 310 that generates a traditional ECG
trace from the signals detected by the pair of electrodes 114, the
P Wave Detection Module 320 for detecting or identifying the P wave
portion of the ECG trace, and the Interpretive Module 330. As
discussed above with respect to the system 200, the ECG Trace
Generator Module 310 may record the ECG trace generated
thereby.
Optionally, the P Wave Detection Module 320 may include
instructions for identifying the QRS complex as well as the P wave
portion of the ECG trace. Further, the P Wave Detection Module 320
may include instructions for determining a deflection value for an
initial upwardly deflecting portion of a single P wave preceding a
downwardly deflecting portion. The P Wave Detection Module 320 may
also include instructions for determining a positive/total
deflection ratio of the largest positive deflection value for the
initial upwardly deflecting portion of the P wave to the deflection
value for the entire P wave.
Like the Interpretive Module 330 of the system 200, the
Interpretive Module 330 of the system 400 determines the deflection
value of the P wave detected by a pair of electrodes (i.e., the
pair of electrodes 114). However, other functions performed by the
Interpretive Module 330 may differ in system 400 from those
performed by the Interpretive Module 330 in system 200. The
Interpretive Module 330 directs the CPU 210 to store the deflection
value of the P wave detected by the pair of electrodes 114 in the
proximal SVC in memory 220. The Interpretive Module 330 may receive
input from the user or operator via the user interface 410
instructing the Interpretive Module 330 to store the deflection
value.
The Interpretive Module 330 also includes instructions for
performing the method 140, 190, and/or the method 600. With respect
to the method 140 (see FIG. 4), the Interpretive Module 330 may
determine the ratio of the deflection value of the currently
observed P wave to the reference deflection value. The Interpretive
Module 330 may compare this ratio to the first predefined threshold
(e.g., about 1.5). If the ratio is less than or equal to the first
predefined threshold, the Interpretive Module 330 determines the
tip 112 is in the SVC. Further, if the determination is made in
block 143, the Interpretive Module 330 may signal the user or
operator to advance the tip 112. If the determination is made in
block 145, the Interpretive Module 330 may signal the user or
operator to stop withdrawing the tip 112.
If the ratio is greater than the first predefined threshold, the
Interpretive Module 330 determines the tip 112 is not in a desired
location and instructs the user interface 410 to signal the user or
operator to withdraw the tip.
The Interpretive Module 330 may compare the ratio to the second
predefined threshold value (e.g., about 2.0) If the ratio is less
than or equal to the second predefined threshold value, the
Interpretive Module 330 determines the tip 112 is in the distal SVC
near the SA node or in the atrium near the SA node. If the ratio is
greater than the second predefined threshold value, the
Interpretive Module 330 determines the tip 112 is in the
atrium.
Optionally, the Interpretive Module 330 may determine the ratio of
the deflection value of the current P wave detected by the pair of
electrodes 114 to the reference atrium deflection value. The
Interpretive Module 330 may compare this ratio to the third
predefined threshold value (e.g., about 0.5) to determine whether
the tip 112 is in the atrium or the ventricle.
With respect to the method 190 (see FIG. 6), the Interpretive
Module 330 may determine the tip 112 is located within the right
atrium using any method known in the art or disclosed herein. The
Interpretive Module 330 then calculates the positive/negative
deflection ratio and compares this ratio to the first predetermined
threshold value (e.g., about 0.30). If the positive/negative
deflection ratio is less than the first predetermined threshold
value, the Interpretive Module 330 determines the tip 112 is in the
upper right atrium. On the other hand, if the positive/negative
deflection ratio is greater than or equal to the first
predetermined threshold value, the Interpretive Module 330 compares
positive/negative deflection ratio to the second predetermined
threshold value (e.g., about 1.30). If the positive/negative
deflection ratio is greater than the second predetermined threshold
value, the Interpretive Module 330 determines the tip 112 is in the
lower atrium. Otherwise, if the positive/negative deflection ratio
is greater than or equal to the first predetermined threshold value
and less than or equal to the second predetermined threshold value,
the Interpretive Module 330 determines the tip 112 is in the mid
atrium.
With respect to the method 600 (see FIGS. 11A and 11B), the
Interpretive Module 330 may store a reference deflection value and
determine the deflection ratio of the deflection value of the
currently observed P wave to the reference deflection value. After
the tip 112 is withdrawn or advanced, the Interpretive Module 330
may determine the current deflection ratio of the deflection value
of the currently observed P wave to the reference deflection value.
The deflection ratio determined before the tip 112 was withdrawn or
advanced is stored by the Interpretive Module 330 as a previous
deflection ratio.
Each time the tip 112 is moved (e.g., advanced or withdrawn), the
Interpretive Module 330 determines whether the current deflection
ratio is the largest observed since the CVC 100 was inserted into
the venous system, and if the current deflection ratio is the
largest deflection ratio observed, stores the current deflection
ratio as the maximum deflection ratio.
The Interpretive Module 330 compares the current deflection ratio
to the previous deflection ratio. If the current deflection ratio
is less than or equal to the previous deflection ratio, the
Interpretive Module 330 determines the tip 112 has been advanced
too far and may signal the user to withdraw the CVC 100. Then, the
Interpretive Module 330 determines whether the tip 112 has been
withdrawn far enough. The Interpretive Module 330 may determine the
tip 112 has been withdrawn far enough when the positive/total
deflection ratio is less than a predetermined fraction (e.g., one
quarter, one eighth, etc.). Otherwise, the tip 112 has not been
withdrawn far enough. If the tip 112 has not been withdrawn far
enough, the Interpretive Module 330 signals the user to withdraw
the tip 112.
If the tip 112 has been withdrawn far enough, the Interpretive
Module 330 determines whether the current deflection ratio is
approximately equal to the maximum deflection ratio. If the current
deflection ratio is not approximately equal to the maximum
deflection ratio, the Interpretive Module 330 determines the tip
112 has been withdrawn too far and signals the user to advance the
CVC 100.
As mentioned above, the Interpretive Module 330 may compare current
deflection ratio to the previous deflection ratio. If the current
deflection ratio is greater than the previous deflection ratio, the
Interpretive Module 330 determines whether the current deflection
ratio is less than a maximum threshold value (e.g., 8.0). If the
current deflection ratio is less than the maximum threshold value,
the Interpretive Module 330 determines the tip 112 has not been
advanced far enough and signals the user to advance the CVC
100.
If instead the current deflection ratio is greater than or equal to
the maximum threshold value, the interpretive Module 330 determines
whether the current deflection ratio is approximately equal to the
maximum threshold value. If the current deflection ratio is not
approximately equal to the maximum threshold value, the
interpretive Module 330 determines the tip 112 has been advanced
too far and signals the user to withdraw the CVC 100. After the tip
112 is withdrawn, the interpretive Module 330 determines whether
the current deflection ratio is approximately equal to the maximum
threshold value.
If the current deflection ratio is not approximately equal to the
maximum threshold value, the Interpretive Module 330 determines
whether the current deflection ratio is less than the maximum
threshold value (indicating the tip 112 has been withdrawn too
far). If the current deflection ratio is less than the maximum
threshold value, the Interpretive Module 330 determines the tip 112
has been withdrawn too far and signals the user to advance the CVC
100. On the other hand, if the current deflection ratio is still
greater than the maximum threshold value, the Interpretive Module
330 determines the tip 112 has not been withdrawn far enough and
signals the user to withdraw the CVC 100.
Optionally, whenever the current deflection ratio is approximately
equal to the maximum deflection ratio or the maximum threshold
value, the Interpretive Module 330 may signal the user to stop
moving (e.g., advancing or withdrawing) the CVC 100.
With respect to the methods 140, 190, and 600, the instructions in
the Interpretive Module 330 direct the CPU 210 to use the user
interface 410 to communicate whether the tip 112 should be
withdrawn to the user. Furthers the instructions in the
Interpretive Module 330 direct the CPU 210 to use the user
interface 410 to communicate the tip 112 may be advanced. Because
the Interpretive Module 330 may interpret the P wave to obtain the
deflection values, compare the deflection values, and provide the
operator with immediate real-time feedback, the operator need not
interpret the actual ECG waveforms.
Optionally, the system 400 could be coupled to a prior art
navigational system, such as a VIASYS MedSystems NAVIGATOR.RTM.
BioNavigation.RTM. system, manufactured by VIASYS Healthcare Inc.
of Conshohocken, Pa., which is principally used to guide
peripherally placed lines, such as a peripherally inserted central
catheter ("PICC") Such systems determine the location of a PICC
line using magnetic fields that are generated by a detector, and
detected by a magnetically activated position sensor located in the
tip of a stylet inserted inside the PICC near its tip. By way of a
non-limiting example, the detector may include a NAVIGATOR.RTM.
electronic locating instrument configured to emit low-level,
high-frequency magnetic fields. Also by way of a non-limiting
example, the stylet may include a MAPCath.RTM. Sensor Stylet also
manufactured by VIASYS Healthcare Inc.
The sensor in the tip of the stylet is activated by the magnetic
field emitted by the detector. The sensor is operable to output its
location via a wire coupled to the sensor and extending
longitudinally along the PICC to the detector, which is configured
to interpret the signal and communicate the location of the tip to
the user or operator. As mentioned above, because such navigational
systems depend upon a relationship between surface landmarks and
anatomic locations, they cannot be used to determine the location
of the tip 112 of the CVC 100 with sufficient accuracy. However,
the system 400 may be used, in conjunction with a navigational
system to improve the accuracy of the navigational system.
By way of non-limiting examples, additional prior art navigational
systems include the Sherlock Tip Location System used with the
stylet provided in Bard Access Systems PICC kits both of which are
manufactured by C. R. Bard, Inc. of Salt Lake City, Utah, the
CathRite.TM. system manufactured by Micronix Pty. Ltd. of
Australia, and the like. As is apparent to those of ordinary skill
in the art, the present teaching may be combined with one or more
of these additional exemplary navigational systems and used to
improve the accuracy of those systems.
In further embodiments, the teachings provided herein may be
expanded to use electrophysiology procedures for navigating other
bodily channels. For example, in the prior art, ECG guidance
techniques have been used to place feeding tubes. Because the QRS
complex measured in the stomach is upright but in a post pyloric
area (first part of the duodenum, beyond the stomach) the ORS
complex is down-going, one or more threshold deflection values may
be determined and used to determine the placement of the tip of the
feeding tube.
The foregoing described embodiments depict different components
contained within, or connected with, different other components. It
is to be understood that such depicted architectures are merely
exemplary, and that in fact many other architectures can be
implemented which achieve the same functionality. In a conceptual
sense, any arrangement of components to achieve the same
functionality is effectively "associated" such that the desired
functionality is achieved. Hence, any two components herein
combined to achieve a particular functionality can be seen as
"associated with" each other such that the desired functionality is
achieved, irrespective of architectures or intermedial components.
Likewise, any two components so associated can also be viewed as
being "operably connected", or "operably coupled", to each other to
achieve the desired functionality.
While particular embodiments of the present invention have been
shown and described, it will be obvious to those skilled in the art
that, based upon the teachings herein, changes and modifications
may be made without departing from this invention and its broader
aspects and, therefore, the appended claims are to encompass within
their scope all such changes and modifications as are within the
true spirit and scope of this invention. Furthermore, it is to be
understood that the invention is solely defined by the appended
claims. It will be understood by those within the art that, in
general, terms used herein, and especially in the appended claims
(e.g., bodies of the appended claims) are generally intended as
"open" terms (e.g., the term "including" should be interpreted as
"including but not limited to," the term "having" should be
interpreted as "having at least," the term "includes" should be
interpreted as "includes but is not limited to," etc.). It will be
further understood by those within the art that if a specific
number of an introduced claim recitation is intended, such an
intent will be explicitly recited in the claim, and in the absence
of such recitation no such intent is present. For example, as an
aid to understanding, the following appended claims may contain
usage of the introductory phrases "at least one" and "one or more"
to introduce claim recitations. However, the use of such phrases
should not be construed to imply that the introduction of a claim
recitation by the indefinite articles "a" or "an" limits any
particular claim containing such introduced claim recitation to
inventions containing only one such recitation, even when the same
claim includes the introductory phrases "one or more" or "at least
one" and indefinite articles such as "a" or "an" (e.g., "a" and/or
"an" should typically be interpreted to mean "at least one" or "one
or more"); the same holds true for the use of definite articles
used to introduce claim recitations. In addition, even if a
specific number of an introduced claim recitation is explicitly
recited, those skilled in the art will recognize that such
recitation should typically be interpreted to mean at least the
recited number (e.g., the bare recitation of "two recitations,"
without other modifiers, typically means at feast two recitations,
or two or more recitations).
Accordingly, the invention is not limited except as by the appended
claims.
* * * * *
References